View source for Pain

{{Short description|Type of distressing feeling}}
{{About|physical pain|mental or emotional pain|Psychological pain|other uses|Pain (disambiguation)}}
{{Use dmy dates|date=September 2022}}
{{Infobox medical condition
| name = 
| image = Wrist pain.jpg
| caption = An illustration of [[wrist pain]]
| specialty = [[Neurology]]<br />[[Pain medicine]]
| symptoms = Unpleasant sensory and emotional sensations<ref name="IASPdefinition">{{cite journal | vauthors = Raja SN, Carr DB, Cohen M, Finnerup NB, Flor H, Gibson S, Keefe FJ, Mogil JS, Ringkamp M, Sluka KA, Song XJ, Stevens B, Sullivan MD, Tutelman PR, Ushida T, Vader K | display-authors = 6 | title = The revised International Association for the Study of Pain definition of pain: concepts, challenges, and compromises | language = en-US | journal = Pain | volume = 161 | issue = 9 | pages = 1976–1982 | date = September 2020 | pmid = 32694387 | pmc = 7680716 | doi = 10.1097/j.pain.0000000000001939 | doi-access = free }}</ref>
| complications = 
| onset = 
| duration = Typically depends on the cause
| types = Physical, [[Psychological pain|psychological]], [[Psychogenic pain|psychogenic]]
| causes = 
| risks = 
| diagnosis = 
| differential = 
| prevention = 
| treatment = 
| medication = [[Analgesic]]s
| prognosis = 
| frequency = 
| deaths = 
}}

'''Pain''' is a [[suffering|distressing feeling]] often caused by intense or damaging [[Stimulus (physiology)|stimuli]]. The [[International Association for the Study of Pain]] defines pain as "an unpleasant [[sense|sensory]] and [[emotion]]al experience associated with, or resembling that associated with, actual or potential tissue damage."<ref name="IASPdefinition"/>

Pain motivates [[organism]]s to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future.<ref>{{Cite book|title=Understanding Pain: Exploring the Perception of Pain| vauthors = Cervero F |date=2012 |publisher=MIT Press |isbn=978-0-262-30543-3 |location=Cambridge, Mass. |pages=Chapter 1 |oclc=809043366 }}</ref> [[Congenital insensitivity to pain]] may result in reduced [[life expectancy]].<ref name="pmid12583863"/> Most pain resolves once the [[noxious stimulus]] is removed and the body has healed, but it may persist despite removal of the stimulus and apparent healing of the body. Sometimes pain arises in the absence of any detectable stimulus, damage or disease.<ref name="Raj_2007">{{cite book |vauthors=Raj PP |title=In: The Handbook of Chronic Pain |publisher=Nova Biomedical Books |year=2007 |isbn=978-1-60021-044-0 |chapter=Taxonomy and classification of pain |chapter-url=https://books.google.com/books?id=ZG4Svh_UL3UC&pg=PA41 |access-date=3 February 2016 |archive-date=30 March 2021 |archive-url=https://web.archive.org/web/20210330014627/https://books.google.com/books?id=ZG4Svh_UL3UC&pg=PA41 |url-status=live }}</ref>

Pain is the most common reason for physician consultation in most developed countries.<ref name="painreview">{{cite journal | vauthors = Debono DJ, Hoeksema LJ, Hobbs RD | title = Caring for patients with chronic pain: pearls and pitfalls | journal = The Journal of the American Osteopathic Association | volume = 113 | issue = 8 | pages = 620–7 | date = August 2013 | pmid = 23918913 | doi = 10.7556/jaoa.2013.023 | doi-access = free }}</ref><ref name="Turk & Dennis 2004">{{cite journal | vauthors = Turk DC, Dworkin RH | title = What should be the core outcomes in chronic pain clinical trials? | journal = Arthritis Research & Therapy | volume = 6 | issue = 4 | pages = 151–4 | year = 2004 | pmid = 15225358 | pmc = 464897 | doi = 10.1186/ar1196 | doi-access = free }}</ref> It is a major symptom in many medical conditions, and can interfere with a person's [[quality of life]] and general functioning.<ref name= Breivik2008>{{cite journal | vauthors = Breivik H, Borchgrevink PC, Allen SM, Rosseland LA, Romundstad L, Hals EK, Kvarstein G, Stubhaug A | title = Assessment of pain | journal = British Journal of Anaesthesia | volume = 101 | issue = 1 | pages = 17–24 | date = July 2008 | pmid = 18487245 | doi = 10.1093/bja/aen103 | doi-access = free }}</ref> People in pain experience impaired concentration, [[working memory]], [[Cognitive flexibility|mental flexibility]], problem solving and information processing speed, and are more likely to experience irritability, depression, and anxiety.

Simple pain medications are useful in 20% to 70% of cases.<ref>{{cite journal | vauthors = Moore RA, Wiffen PJ, Derry S, Maguire T, Roy YM, Tyrrell L | title = Non-prescription (OTC) oral analgesics for acute pain – an overview of Cochrane reviews | journal = The Cochrane Database of Systematic Reviews | volume = 11 | issue = 11 | article-number = CD010794 | date = November 2015 | pmid = 26544675 | pmc = 6485506 | doi = 10.1002/14651858.CD010794.pub2 }}</ref> Psychological factors such as [[social support]], [[cognitive behavioral therapy]], excitement, or distraction can affect pain's intensity or unpleasantness.<ref name="Eisenberger_2005">{{cite book |title=The Social Outcast: Ostracism, Social Exclusion, Rejection, & Bullying (Sydney Symposium of Social Psychology) |vauthors=Eisenberger NI, Lieberman M |publisher=Psychology Press |year=2005 |isbn=978-1-84169-424-5 |veditors=Williams KD |location=East Sussex |pages=131–150 |chapter=Why it hurts to be left out: The neurocognitive overlap between physical and social pain |doi=10.4324/9780203942888-14 |chapter-url=https://www.academia.edu/621614 |archive-date=10 July 2024 |access-date=18 February 2024 |archive-url=https://web.archive.org/web/20240710180118/https://www.academia.edu/621614 |url-status=live }}</ref><ref name="Mind-Body Therapies for Opioid-Trea">{{cite journal | vauthors = Garland EL, Brintz CE, Hanley AW, Roseen EJ, Atchley RM, Gaylord SA, Faurot KR, Yaffe J, Fiander M, Keefe FJ | display-authors = 6 | title = Mind-Body Therapies for Opioid-Treated Pain: A Systematic Review and Meta-analysis | journal = JAMA Internal Medicine | volume = 180 | issue = 1 | pages = 91–105 | date = January 2020 | pmid = 31682676 | pmc = 6830441 | doi = 10.1001/jamainternmed.2019.4917 }}</ref>

== Etymology ==
First attested in English in 1297, the word ''peyn'' comes from the [[Old French]] ''peine'', in turn from [[Latin]] ''poena'' meaning "punishment, penalty"<ref>{{cite web | vauthors = Lewis CT, Short C | work = A Latin Dictionary | url = https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3Aentry%3Dpoena | title = Poena | archive-url = https://web.archive.org/web/20110513202944/https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3Aentry%3Dpoena| archive-date = 13 May 2011 | via = Perseus Digital Library }}</ref><ref>{{Cite journal |last1=Lavoie |first1=Anne |last2=Toledo |first2=Paloma |date=2013-09-01 |title=Multimodal Postcesarean Delivery Analgesia |url=https://www.sciencedirect.com/science/article/pii/S0095510813000638 |journal=Clinics in Perinatology |series=Pain Management in the Peripartum Period |language=en |volume=40 |issue=3 |pages=443–455 |doi=10.1016/j.clp.2013.05.008 |pmid=23972750 |issn=0095-5108|url-access=subscription }}</ref> (also meaning "torment, hardship, suffering" in Late Latin) and that from [[Greek language|Greek]] ποινή (''poine''), generally meaning "price paid, penalty, punishment".<ref>{{cite web | url = https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dpoinh%2F | title = ποινή | archive-url = https://web.archive.org/web/20110513202951/https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dpoinh%2F| archive-date = 13 May 2011 | vauthors = Liddell HG, Scott R | work = A Greek-English Lexicon | via = Perseus Digital Library }}</ref><ref>{{cite web | url = https://www.etymonline.com/index.php?term=pain | title = Pain | archive-url = https://web.archive.org/web/20110728085534/https://www.etymonline.com/index.php?term=pain| archive-date=28 July 2011 | via = Online Etymology Dictionary }}</ref>

== Classification ==
In many cases, pain fits into one or a combination of three categories:<ref>{{Cite web|url=https://www.ninds.nih.gov/health-information/disorders/pain|title=Pain &#124; National Institute of Neurological Disorders and Stroke|website=www.ninds.nih.gov|access-date=12 March 2025|archive-date=4 March 2025|archive-url=https://web.archive.org/web/20250304174721/https://www.ninds.nih.gov/health-information/disorders/pain|url-status=live}}</ref>

* Nociceptive pain (caused by [[inflamed]] or damaged tissue that activates pain sensors called [[nociceptors]]).<ref name="Treede-2015">{{Cite journal|last1=Treede|first1=Rolf-Detlef|last2=Rief|first2=Winfried|last3=Barke|first3=Antonia|last4=Aziz|first4=Qasim|last5=Bennett|first5=Michael I.|last6=Benoliel|first6=Rafael|last7=Cohen|first7=Milton|last8=Evers|first8=Stefan|last9=Finnerup|first9=Nanna B.|date=June 2015|title=A classification of chronic pain for ICD-11|journal=Pain|volume=156|issue=6|pages=1003–1007|doi=10.1097/j.pain.0000000000000160|issn=1872-6623|pmc=4450869|pmid=25844555}}</ref> Nociceptive pain is divided into "superficial" and "deep" pain. Deep pains are divided into two parts: "deep physical" and "deep visceral" pain.<ref>{{cite book|vauthors=Coda BA, Bonica JJ|veditors=Loeser D, Bonica JJ|title=Bonica's management of pain|edition=3|year=2001|publisher=Lippincott Williams & Wilkins|isbn=978-0-443-05683-3|location=Philadelphia|chapter=General considerations of acute pain|chapter-url-access=registration|chapter-url=https://archive.org/details/painmanagementin0000main}}</ref>

* [[Neuropathic pain]] (caused by damage or malfunction of the [[nervous system]]).<ref name="Treede-2015" /> Neuropathic pain is divided into "[[Peripheral nervous system|peripheral]]" (the source being the [[peripheral nervous system]]) and "[[Central nervous system|central]]" (being from brain and spinal cord).<ref name="Bogduk1994">{{cite book |url=https://archive.org/details/classificationof0000unse_o5f1/page/212 |title=Classification of chronic pain: descriptions of chronic pain syndromes and definitions of pain terms |vauthors=Bogduk N, Merskey H |publisher=IASP Press |year=1994 |isbn=978-0-931092-05-3 |edition=second |location=Seattle |page=[https://archive.org/details/classificationof0000unse_o5f1/page/212 212]}}</ref><ref>{{cite book|title=Diagnostic Methods for Neuropathic Pain: A Review of Diagnostic Accuracy Rapid Response Report: Summary with Critical Appraisal.|publisher=Canadian Agency for Drugs and Technologies in Health|date=April 2015|pmid=26180859}}</ref> [[Peripheral neuropathy]] is often described as "burning", "tingling", "electrical", "stabbing", or "pins and needles".<ref name="Paice2003">{{cite journal |vauthors=Paice JA |date=Jul–Aug 2003 |title=Mechanisms and management of neuropathic pain in cancer |url=http://www.supportiveoncology.net/journal/articles/0102107.pdf |journal=The Journal of Supportive Oncology |volume=1 |issue=2 |pages=107–120 |pmid=15352654 |archive-url=https://web.archive.org/web/20100107161021/http://www.supportiveoncology.net/journal/articles/0102107.pdf |archive-date=2010-01-07 |access-date=2010-05-03}}</ref>

*[[Nociplastic pain]] is pain that arises despite no clear evidence of tissue or somatosensory system damage causing the pain.<ref name="L">{{Cite journal |vauthors=Fitzcharles MA, Cohen SP, Clauw DJ, Littlejohn G, Usui C, Häuser W |date=May 2021 |title=Nociplastic pain: towards an understanding of prevalent pain conditions |journal=Lancet |volume=397 |issue=10289 |pages=2098–2110 |doi=10.1016/S0140-6736(21)00392-5 |pmid=34062144 |s2cid=235245552}}</ref>


In 1994, the [[International Association for the Study of Pain]] recommended using specific features to describe a patient's pain:
# Region of the body involved (e.g., abdomen or lower limbs)
# System whose dysfunction may be causing the pain (e.g., nervous or gastrointestinal systems)
# Duration and pattern of occurrence
# Intensity
# Cause<ref name= Merskey_Bogduk>{{cite book |vauthors=Merskey H, Bogduk N |title=Classification of Chronic Pain |edition=2 nd |location=Seattle |publisher=International Association for the Study of Pain |year=1994 |isbn=978-0-931092-05-3 |pages=[https://archive.org/details/classificationof0000unse_o5f1/page/3 3 & 4] |url=https://archive.org/details/classificationof0000unse_o5f1/page/3 }}</ref>

=== Chronic versus acute ===
{{main|Chronic pain}}

Pain is usually transitory, lasting only until the noxious stimulus is removed or the underlying damage or pathology has healed. But some painful conditions, such as [[rheumatoid arthritis]], [[peripheral neuropathy]], [[Cancer pain|cancer]], and [[idiopathic]] pain, may persist for years. Pain that lasts a long time is called "[[Chronic pain|chronic]]" or "persistent", and pain that resolves quickly is called "[[Acute (medicine)|acute]]". Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time between onset and resolution; the two most commonly used markers being 3 months and 6 months since the onset of pain,<ref name = Turk&Okifuji2001>{{cite book | vauthors = Turk DC, Okifuji A | veditors = Bonica JJ, Loeser JD, Chapman CR, Turk DC |title=Bonica's management of pain |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |year=2001 |isbn=978-0-7817-6827-6 |chapter=Pain terms and taxonomies of pain}}</ref> though some theorists and researchers have placed the transition from acute to chronic pain at 12 months.<ref name="isbn0-443-05683-8"/>{{rp|93}} Others apply "acute" to pain that lasts less than 30 days, "chronic" to pain of at least six months' duration, and "subacute" to pain that lasts from one to six months.<ref name=Thienhaus1>{{cite book | vauthors = Thienhaus O, Cole BE | veditors = Weiner R |title=Pain management: a practical guide for clinicians | url = https://archive.org/details/painmanagementpr00wein | url-access = limited |publisher=CRC Press |location=Boca Raton |year=2002 |pages=[https://archive.org/details/painmanagementpr00wein/page/n60 28] |isbn=978-0-8493-2262-4 |chapter=Classification of pain}}</ref> A popular alternative definition of "chronic pain", involving no arbitrarily fixed duration, is "pain that extends beyond the expected period of healing".<ref name = Turk&Okifuji2001/> Chronic pain may be classified as "[[cancer pain|cancer-related]]" or "benign."<ref name=Thienhaus1/>

=== Allodynia ===
[[Allodynia]] is pain experienced in response to an ordinarily painless stimulus.<ref name=":0">{{cite journal | vauthors = Jensen TS, Finnerup NB | title = Allodynia and hyperalgesia in neuropathic pain: clinical manifestations and mechanisms | journal = The Lancet. Neurology | volume = 13 | issue = 9 | pages = 924–935 | date = September 2014 | pmid = 25142459 | doi = 10.1016/s1474-4422(14)70102-4 | s2cid = 25011309 }}</ref> It has no biological function and is classified by characteristics of the stimuli as cold, heat, touch, pressure or a pinprick.<ref name=":0"/><ref name="Lolignier 133–139">{{cite journal | vauthors = Lolignier S, Eijkelkamp N, Wood JN | title = Mechanical allodynia | journal = Pflügers Archiv | volume = 467 | issue = 1 | pages = 133–139 | date = January 2015 | pmid = 24846747 | pmc = 4281368 | doi = 10.1007/s00424-014-1532-0 }}</ref>

=== Phantom ===
{{Main|Phantom pain}}
[[Phantom pain]] is pain felt in a part of the body that has been [[amputated]] or from which the brain no longer receives signals. It is a type of neuropathic pain.<ref name="pmid10863043">{{cite journal | vauthors = Kooijman CM, Dijkstra PU, Geertzen JH, Elzinga A, van der Schans CP | title = Phantom pain and phantom sensations in upper limb amputees: an epidemiological study | journal = Pain | volume = 87 | issue = 1 | pages = 33–41 | date = July 2000 | pmid = 10863043 | doi = 10.1016/S0304-3959(00)00264-5 | s2cid = 7565030 | url = https://research.rug.nl/en/publications/phantom-pain-and-phantom-sensations-in-upper-limb-amputees(8dd1fc12-cc0d-400b-aef1-72ed0443f9ad).html }}{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

The [[prevalence]] of phantom pain in upper limb amputees is nearly 82%, and in lower limb amputees is 54%.<ref name="pmid10863043"/> One study found that eight days after amputation, 72% of patients had phantom limb pain, and six months later, 67% reported it.<ref name="pmid6657285">{{cite journal | vauthors = Jensen TS, Krebs B, Nielsen J, Rasmussen P | title = Phantom limb, phantom pain and stump pain in amputees during the first 6 months following limb amputation | journal = Pain | volume = 17 | issue = 3 | pages = 243–256 | date = November 1983 | pmid = 6657285 | doi = 10.1016/0304-3959(83)90097-0 | s2cid = 10304696 }}</ref><ref name="pmid3991231">{{cite journal | vauthors = Jensen TS, Krebs B, Nielsen J, Rasmussen P | title = Immediate and long-term phantom limb pain in amputees: incidence, clinical characteristics and relationship to pre-amputation limb pain | journal = Pain | volume = 21 | issue = 3 | pages = 267–278 | date = March 1985 | pmid = 3991231 | doi = 10.1016/0304-3959(85)90090-9 | s2cid = 24358789 }}</ref> Some amputees experience continuous pain that varies in intensity or quality; others experience several bouts of pain per day, or it may reoccur less often. It is often described as shooting, crushing, burning, or cramping. If the pain is continuous for an extended period, parts of the intact body may become sensitized, so touching them evokes pain in the phantom limb. Phantom limb pain may accompany [[urination]] or [[defecation]].<ref name = "The challenge of pain">{{cite book | vauthors = Wall PD, Melzack R |title=The challenge of pain |edition=2nd |publisher=Penguin Books |location=New York |year=1996 |isbn=978-0-14-025670-3}}</ref>{{rp|61–69}}

[[Local anesthetic]] injections into the nerves or sensitive areas of the stump may relieve pain for days, weeks, or sometimes permanently, despite the drug wearing off in a matter of hours, and small injections of [[:wikt:hypertonic|hypertonic]] saline into the soft tissue between vertebrae produces local pain that radiates into the phantom limb for ten minutes or so and may be followed by hours, weeks, or even longer of partial or total relief from phantom pain. Vigorous vibration or electrical stimulation of the stump, or current from electrodes surgically implanted onto the spinal cord, all produce relief in some patients.<ref name = "The challenge of pain"/>{{rp|61–69}}

[[Mirror box]] therapy produces the illusion of movement and touch in a phantom limb, which in turn may cause a reduction in pain.<ref name="pmid8637922">{{cite journal | vauthors = Ramachandran VS, Rogers-Ramachandran D | title = Synaesthesia in phantom limbs induced with mirrors | journal = Proceedings. Biological Sciences | volume = 263 | issue = 1369 | pages = 377–386 | date = April 1996 | pmid = 8637922 | doi = 10.1098/rspb.1996.0058 | bibcode = 1996RSPSB.263..377R | s2cid = 4819370 }}</ref>

[[Paraplegia]], the loss of sensation and voluntary motor control after serious spinal cord damage, may be accompanied by [[girdle pain]] at the level of the spinal cord damage, [[visceral pain]] evoked by a filling bladder or bowel, or, in five to ten percent of people with paraplegia, phantom body pain in areas of complete sensory loss. This phantom body pain is initially described as burning or tingling but may evolve into severe crushing or pinching pain or the sensation of fire running down the legs or of a knife twisting in the flesh. Onset may or may not occur immediately years after the disabling injury. Surgical treatment rarely provides lasting relief.<ref name = "The challenge of pain"/>{{rp|61–69}}

=== Breakthrough{{anchor|Breakthrough_pain}} ===
Breakthrough pain is transitory pain that comes on suddenly and is not alleviated by the patient's regular [[pain management]]. It is common in cancer patients who often have background pain that is generally well-controlled by medications but who also sometimes experience bouts of severe pain that, from time to time, "breaks through" the medication. The characteristics of breakthrough [[cancer pain]] vary from person to person and according to the cause. Management of breakthrough pain can entail intensive use of [[opioid]]s, including [[fentanyl]].<ref>{{cite journal | vauthors = Mishra S, Bhatnagar S, Chaudhary P, Rana SP | title = Breakthrough cancer pain: review of prevalence, characteristics and management | journal = Indian Journal of Palliative Care | volume = 15 | issue = 1 | pages = 14–18 | date = January 2009 | pmid = 20606850 | pmc = 2886208 | doi = 10.4103/0973-1075.53506 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Caraceni A, Hanks G, Kaasa S, Bennett MI, Brunelli C, Cherny N, Dale O, De Conno F, Fallon M, Hanna M, Haugen DF, Juhl G, King S, Klepstad P, Laugsand EA, Maltoni M, Mercadante S, Nabal M, Pigni A, Radbruch L, Reid C, Sjogren P, Stone PC, Tassinari D, Zeppetella G | title = Use of opioid analgesics in the treatment of cancer pain: evidence-based recommendations from the EAPC | journal = The Lancet. Oncology | volume = 13 | issue = 2 | pages = e58–68 | date = February 2012 | pmid = 22300860 | doi = 10.1016/S1470-2045(12)70040-2 | url = https://www.fadin.org/Documenti/164/Recommendations_EAPC_2012.pdf | archive-url = https://web.archive.org/web/20141019205001/https://www.fadin.org/Documenti/164/Recommendations_EAPC_2012.pdf | archive-date = 19 October 2014 | access-date = 7 March 2022 }}</ref>

=== Asymbolia and insensitivity ===
{{Main|Pain asymbolia|Congenital insensitivity to pain}}
{{Redirect|Painless}}
[[File:No pain. Science Museum Painless Exhibition Series.webm|thumb|A patient and doctor discuss congenital insensitivity to pain.]]
The ability to experience pain is essential for protection from injury and recognition of the presence of injury. Episodic [[analgesia]] may occur under special circumstances, such as in the excitement of sport or war: a soldier on the battlefield may feel no pain for many hours from a traumatic amputation or other severe injury.<ref>{{cite book | vauthors = Beecher HK | date = 1959 | title = Measurement of subjective responses | url = https://archive.org/details/measurementofsub0000beec | url-access = registration | location = New York | publisher = Oxford University Press}} cited in {{cite book | vauthors = Melzack R, Wall PD | date = 1996 | title = The challenge of pain | edition = 2nd | location = London | publisher = Penguin | page = 7 | isbn = 978-0-14-025670-3}}</ref>

Although unpleasantness is an essential part of the [[International Association for the Study of Pain|IASP]] definition of pain,<ref name="IASPdef">{{cite web|title=International Association for the Study of Pain: Pain Definitions|url=https://www.iasp-pain.org/Taxonomy|archive-url=https://web.archive.org/web/20150113000208/https://www.iasp-pain.org/Taxonomy|archive-date=13 January 2015|access-date=12 January 2015|quote=Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage}} [https://etc.ch/ZTKs Alt URL]{{Dead link|date=February 2022 |bot=InternetArchiveBot |fix-attempted=yes }} Derived from {{cite journal|vauthors=Bonica JJ|date=June 1979|title=The need of a taxonomy|journal=Pain|volume=6|issue=3|pages=247–248|doi=10.1016/0304-3959(79)90046-0|pmid=460931|s2cid=53161389}}</ref> it is possible in some patients to induce a state known as pain asymbolia, described as intense pain devoid of unpleasantness, with [[morphine]] injection or [[psychosurgery]].<ref name=IASP_definitions/> Such patients report pain but are not bothered by it; they recognize the sensation of pain but suffer little or not at all.<ref name="asymbolia">{{cite book | vauthors = Grahek N |title=Feeling pain and being in pain |date=2007 |publisher=MIT Press |location=Cambridge, Mass. |isbn=978-0-262-51732-4 |edition=2nd | url = https://docserver.bis.uni-oldenburg.de/publikationen/bisverlag/2001/grafee01/grafee01.html | archive-url = https://web.archive.org/web/20080927042509/https://docserver.bis.uni-oldenburg.de/publikationen/bisverlag/2001/grafee01/grafee01.html | archive-date = 27 September 2008 }}</ref> Indifference to pain can also rarely be present from birth; these people have normal nerves on medical investigations, and find pain unpleasant, but do not avoid repetition of the pain stimulus.<ref name="pmid12583863">{{cite journal | vauthors = Nagasako EM, Oaklander AL, Dworkin RH | title = Congenital insensitivity to pain: an update | journal = Pain | volume = 101 | issue = 3 | pages = 213–219 | date = February 2003 | pmid = 12583863 | doi = 10.1016/S0304-3959(02)00482-7 | s2cid = 206055264 }}</ref>

Insensitivity to pain may also result from abnormalities in the [[nervous system]]. This is usually the result of [[acquired disorder|acquired]] damage to the nerves, such as [[spinal cord injury]], [[diabetes mellitus]] ([[diabetic neuropathy]]), or [[leprosy]] in countries where that disease is prevalent.<ref name=Brand_1997>{{cite book | vauthors = Brand PW, Yancey P |title=The gift of pain: why we hurt & what we can do about it |publisher=Zondervan Publ |location=Grand Rapids, Mich |year=1997 |isbn=978-0-310-22144-9}}</ref> These individuals are at risk of tissue damage and infection due to undiscovered injuries. People with diabetes-related nerve damage, for instance, sustain poorly healing foot ulcers as a result of decreased sensation.<ref name="pmid15472838">{{cite journal | vauthors = Lipsky BA, Berendt AR, Deery HG, Embil JM, Joseph WS, Karchmer AW, LeFrock JL, Lew DP, Mader JT, Norden C, Tan JS | title = Diagnosis and treatment of diabetic foot infections | journal = Clinical Infectious Diseases | volume = 39 | issue = 7 | pages = 885–910 | date = October 2004 | pmid = 15472838 | doi = 10.1086/424846 | first11 = JS | first10 = C | doi-access = free }}</ref>

A much smaller number of people are insensitive to pain due to an inborn abnormality of the nervous system, known as "[[congenital insensitivity to pain]]".<ref name="pmid12583863"/> Children with this condition incur carelessly-repeated damage to their tongues, eyes, joints, skin, and muscles. Some die before adulthood, and others have a reduced life expectancy.<ref>{{Cite journal |last1=Raina* |first1=Triveni |last2=Dash |first2=Bhagya Ranjan |title=AN INTRODUCTORY APPROACH TO PAIN MANAGEMENT THROUGH AYURVEDA WITH BRIEF HOLISTIC REVIEW |url=https://core.ac.uk/outputs/333809971/?utm_source=pdf&utm_medium=banner&utm_campaign=pdf-decoration-v1 |archive-date=27 August 2024 |access-date=27 August 2024 |archive-url=https://web.archive.org/web/20240827103149/https://core.ac.uk/outputs/333809971/?utm_source=pdf&utm_medium=banner&utm_campaign=pdf-decoration-v1 |url-status=live }}</ref> Most people with congenital insensitivity to pain have one of five [[hereditary sensory and autonomic neuropathy|hereditary sensory and autonomic neuropathies]] (which includes [[familial dysautonomia]] and [[congenital insensitivity to pain with anhidrosis]]).<ref name=Axelrod>{{cite journal | vauthors = Axelrod FB, Hilz MJ | title = Inherited autonomic neuropathies | journal = Seminars in Neurology | volume = 23 | issue = 4 | pages = 381–390 | date = December 2003 | pmid = 15088259 | doi = 10.1055/s-2004-817722 | s2cid = 260317729 }}</ref> These conditions feature decreased sensitivity to pain together with other neurological abnormalities, particularly of the [[autonomic nervous system]].<ref name="pmid12583863"/><ref name=Axelrod/> A very rare syndrome with isolated congenital insensitivity to pain has been linked with mutations in the ''[[SCN9A]]'' gene, which codes for a sodium channel ([[Nav1.7|Na<sub>v</sub>1.7]]) necessary in conducting pain nerve stimuli.<ref name="pmid21041956">{{cite journal | vauthors = Raouf R, Quick K, Wood JN | title = Pain as a channelopathy | journal = The Journal of Clinical Investigation | volume = 120 | issue = 11 | pages = 3745–3752 | date = November 2010 | pmid = 21041956 | pmc = 2965577 | doi = 10.1172/JCI43158 }}</ref>

== Functional effects ==
Experimental subjects challenged by acute pain and patients in chronic pain experience impairments in attention control, [[Working memory|working memory capacity]], [[Cognitive flexibility|mental flexibility]], problem solving, and information processing speed.<ref name=Hart2003>{{cite journal | vauthors = Hart RP, Wade JB, Martelli MF | title = Cognitive impairment in patients with chronic pain: the significance of stress | journal = Current Pain and Headache Reports | volume = 7 | issue = 2 | pages = 116–126 | date = April 2003 | pmid = 12628053 | doi = 10.1007/s11916-003-0021-5 | s2cid = 14104974 }}</ref> Pain is also associated with increased depression, anxiety, fear, and anger.<ref name="pmid19146872">{{cite journal | vauthors = Bruehl S, Burns JW, Chung OY, Chont M | title = Pain-related effects of trait anger expression: neural substrates and the role of endogenous opioid mechanisms | journal = Neuroscience and Biobehavioral Reviews | volume = 33 | issue = 3 | pages = 475–491 | date = March 2009 | pmid = 19146872 | pmc = 2756489 | doi = 10.1016/j.neubiorev.2008.12.003 }}</ref>

{{blockquote|If I have matters right, the consequences of pain will include direct physical distress, unemployment, financial difficulties, marital disharmony, and difficulties in concentration and attention…|[[Harold Merskey]] 2000<ref name="isbn1-55798-646-0">{{cite book |vauthors=Merskey H |veditors=Weisberg JN, Gatchel RJ |title=Personality Characteristics of Patients With Pain |publisher=American Psychological Association (APA) |year=2000 |isbn=978-1-55798-646-7 |chapter=The History of Psychoanalytic Ideas Concerning Pain |chapter-url-access=registration |chapter-url=https://archive.org/details/personalitychara0000unse }}</ref>}}

=== On subsequent negative emotion ===
Although pain is considered to be aversive and unpleasant and is therefore usually avoided, a [[meta-analysis]] which summarized and evaluated numerous studies from various psychological disciplines, found a reduction in [[negative affect]]. Across studies, participants that were subjected to acute physical pain in the laboratory subsequently reported feeling better than those in non-painful control conditions, a finding which was also reflected in physiological parameters.<ref>{{cite journal |vauthors= Bresin K, Kling L, Verona E | year = 2018 | title = The effect of acute physical pain on subsequent negative emotional affect: A meta-analysis | journal = Personality Disorders: Theory, Research, and Treatment | volume = 9 | issue = 3| pages = 273–283 | doi = 10.1037/per0000248 | pmid = 28368146 | pmc = 5624817 }}</ref> A potential mechanism to explain this effect is provided by the [[opponent-process theory]].

==Theory==

=== Historical<!--linked from 'Patrick David Wall'--> ===
{{see also|History of pain theory}}
Before the relatively recent discovery of [[neuron]]s and their role in pain, various body functions were proposed to account for pain. There were several competing early theories of pain among the ancient Greeks: [[Hippocrates]] believed that it was due to an imbalance in [[vital fluid]]s.<ref name=Linton>Linton. Models of Pain Perception. Elsevier Health, 2005. Print.</ref> In the 11th century, [[Avicenna]] theorized that there were a number of feeling senses, including touch, pain, and titillation.<ref name = Dallenbach>{{cite journal | vauthors = Dallenbach KM |title=Pain: History and present status |journal=American Journal of Psychology |date=July 1939 |volume=52 |issue=3 |pages=331–347 |doi=10.2307/1416740|jstor=1416740 }}</ref>

[[File:Jan Baptist Weenix - Portrait of René Descartes.jpg|thumb|right|Portrait of [[René Descartes]] by [[Jan Baptist Weenix]], 1647–1649]]
In 1644, [[René Descartes]] theorized that pain was a disturbance that passed along nerve fibers until the disturbance reached the brain.<ref name=Linton /><ref name=MelzackKatz>{{cite book | vauthors = Melzack R, Katz J | veditors = Craig KD, Hadjistavropoulos T |title=Pain: psychological perspectives |publisher=Lawrence Erlbaum Associates, Publishers |location=Mahwah, N.J |year=2004 |chapter=The Gate Control Theory: Reaching for the Brain |isbn=978-0-415-65061-8}}</ref> The work of Descartes and Avicenna prefigured the 19th-century development of ''specificity theory''. Specificity theory saw pain as "a specific sensation, with its own sensory apparatus independent of touch and other senses".<ref name = Bonica1>{{cite book | vauthors = Bonica JJ |chapter=History of pain concepts and therapies |title=The management of pain |volume=1 |edition=2 |year=1990 |publisher=Lea & Febiger |location=London |page=7 |isbn=978-0-8121-1122-4}}</ref> Another theory that came to prominence in the 18th and 19th centuries was ''intensive theory'', which conceived of pain not as a unique sensory modality, but an emotional state produced by stronger than normal stimuli such as intense light, pressure or temperature.<ref name = Finger>{{cite book | vauthors = Finger S |title=Origins of neuroscience: a history of explorations into brain function |page = 149 |publisher=Oxford University Press |isbn=978-0-19-514694-3|year=2001 |location=US}}</ref> By the mid-1890s, ''specificity'' was backed primarily by physiologists and physicians, and psychologists mostly backed the ''intensive theory''. However, after a series of clinical observations by [[Henry Head]] and experiments by [[Max von Frey]], the psychologists migrated to ''specificity'' almost en masse. By the century's end, most physiology and psychology textbooks presented pain ''specificity'' as fact.<ref name = Dallenbach/><ref name = Bonica1/>

===Modern===
[[File:Schematic of cortical areas involved with pain processing and fMRI.jpg|thumb|right|Regions of the cerebral cortex associated with pain]]
Some sensory fibers do not differentiate between [[Noxious stimulus|noxious]] and non-noxious stimuli, while others (i.e., [[nociceptor]]s) respond only to noxious, high-intensity stimuli. At the peripheral end of the nociceptor, noxious stimuli generate currents that, above a given threshold, send [[action potential|signals]] along the nerve fiber to the spinal cord. The "specificity" (whether it responds to thermal, chemical, or mechanical features of its environment) of a nociceptor is determined by which [[ion channel]]s it expresses at its peripheral end. So far, dozens of types of nociceptor ion channels have been identified, and their exact functions are still being determined.<ref>{{cite journal | vauthors = Woolf CJ, Ma Q | title = Nociceptors{{snd}}noxious stimulus detectors | journal = Neuron | volume = 55 | issue = 3 | pages = 353–364 | date = August 2007 | pmid = 17678850 | doi = 10.1016/j.neuron.2007.07.016 | s2cid = 13576368 | doi-access = free }}</ref>

The pain signal travels from the periphery to the spinal cord along [[A delta fiber|A-delta]] and [[C fiber|C]] fibers. Because the A-delta fiber is thicker than the C fiber, and is thinly sheathed in an electrically insulating material ([[myelin]]), it carries its signal faster (5–30&nbsp;[[Metre per second|m/s]]) than the unmyelinated C fiber (0.5–2&nbsp;m/s).<ref name="Marchand">{{cite book | vauthors = Marchand S | veditors = Beaulieu P, Lussier D, Porreca F, Dickenson A |title=Pharmacology of pain |chapter=Applied pain neurophysiology |publisher=International Association for the Study of Pain Press |location=Seattle |year=2010 |pages=3–26 |isbn=978-0-931092-78-7}}</ref> Pain evoked by the A-delta fibers is described as sharp and is felt first. This is followed by a duller pain—often described as burning—carried by the C fibers.<ref name="Skevington9">{{cite book |vauthors=Skevington S |title=Psychology of pain |publisher=Wiley |location=New York |year=1995 |page=[https://archive.org/details/psychologyofpain0000skev/page/9 9] |isbn=978-0-471-95773-7 |url=https://archive.org/details/psychologyofpain0000skev/page/9 }}</ref> These A-delta and C fibers enter the spinal cord via [[Lissauer's tract]] and connect with spinal cord nerve fibers in the [[central gelatinous substance of the spinal cord]]. These spinal cord fibers then cross the cord via the [[anterior white commissure]] and ascend in the [[spinothalamic tract]]. Before reaching the brain, the spinothalamic tract splits into the [[lateral (anatomy)|lateral]], neospinothalamic tract and the [[medial (anatomy)|medial]], paleospinothalamic tract. The neospinothalamic tract carries the fast, sharp A-delta signal to the ventral posterolateral nucleus of the [[thalamus]]. The paleospinothalamic tract carries the slow, dull C fiber pain signal. Some of the paleospinothalamic fibers peel off in the brain stem—connecting with the reticular formation or midbrain periaqueductal gray—and the remainder terminate in the intralaminar nuclei of the thalamus.<ref name=Skevington1995>{{cite book |vauthors=Skevington SM |year=1995 |title=Psychology of pain |location=Chichester, UK |publisher=Wiley |page=[https://archive.org/details/psychologyofpain0000skev/page/18 18] |isbn=978-0-471-95773-7 |url=https://archive.org/details/psychologyofpain0000skev/page/18 }}</ref>

Pain-related activity in the thalamus spreads to the [[insular cortex]] (thought to embody, among other things, the feeling that distinguishes pain from other [[homeostatic emotion]]s such as itch and nausea) and [[anterior cingulate cortex]] (thought to embody, among other things, the affective/motivational element, the unpleasantness of pain),<ref name= Craig2003a>{{cite journal | vauthors = Craig AD | title = Pain mechanisms: labeled lines versus convergence in central processing | journal = Annual Review of Neuroscience | volume = 26 | pages = 1–30 | year = 2003 | pmid = 12651967 | doi = 10.1146/annurev.neuro.26.041002.131022 | s2cid = 12387848 }}</ref> and pain that is distinctly located also activates the [[primary somatosensory cortex|primary]] and [[secondary somatosensory cortex]].<ref name="Romanelli P, Esposito V.">{{cite journal | vauthors = Romanelli P, Esposito V | title = The functional anatomy of neuropathic pain | journal = Neurosurgery Clinics of North America | volume = 15 | issue = 3 | pages = 257–268 | date = July 2004 | pmid = 15246335 | doi = 10.1016/j.nec.2004.02.010 }}</ref>

Spinal cord fibers dedicated to carrying A-delta fiber pain signals and others that carry both A-delta and C fiber pain signals to the [[thalamus]] have been identified. Other spinal cord fibers, known as [[wide dynamic range neuron]]s, respond to A-delta and C fibers and the much larger, more heavily myelinated A-beta fibers that carry touch, pressure, and vibration signals.<ref name=Marchand/>

[[Ronald Melzack]] and [[Patrick David Wall|Patrick Wall]] introduced their [[gate control theory]] in the 1965 [[Science (journal)|''Science'']] article "Pain Mechanisms: A New Theory".<ref name="pmid5320816">{{cite journal | vauthors = Melzack R, Wall PD | title = Pain mechanisms: a new theory | journal = Science | volume = 150 | issue = 3699 | pages = 971–979 | date = November 1965 | pmid = 5320816 | doi = 10.1126/science.150.3699.971 | url = https://www.hnehealth.nsw.gov.au/__data/assets/pdf_file/0012/70122/pain_mechanisms_20100315013844.pdf | author-link = Ronald Melzack | bibcode = 1965Sci...150..971M | archive-url = https://web.archive.org/web/20120114141747/https://www.hnehealth.nsw.gov.au/__data/assets/pdf_file/0012/70122/pain_mechanisms_20100315013844.pdf | archive-date = 14 January 2012 | author-link2 = Patrick David Wall | access-date = 7 March 2022 }}</ref> The authors proposed that the thin C and A-delta (pain) and large diameter A-beta (touch, pressure, vibration) nerve fibers carry information from the site of injury to two destinations in the [[posterior horn of spinal cord|dorsal horn]] of the spinal cord, and that A-beta fiber signals acting on inhibitory cells in the dorsal horn can reduce the intensity of pain signals sent to the brain.<ref name="MelzackKatz"/>

====Three dimensions of pain====
In 1968, [[Ronald Melzack]] and [[Kenneth L. Casey|Kenneth Casey]] described chronic pain in terms of its three dimensions:
* "sensory-discriminative" (sense of the intensity, location, quality, and duration of the pain),
* "affective-motivational" (unpleasantness and urge to escape the unpleasantness) and
* "cognitive-evaluative" (cognitions such as appraisal, cultural values, distraction, and hypnotic suggestion).

They theorized that pain intensity (the sensory discriminative dimension) and unpleasantness (the affective-motivational dimension) are not simply determined by the magnitude of the painful stimulus, but "higher" cognitive activities can influence perceived intensity and unpleasantness. Cognitive activities may affect both sensory and affective experience, or they may modify primarily the affective-motivational dimension. Thus, excitement in games or war appears to block both the sensory-discriminative and affective-motivational dimensions of pain, while suggestion and placebos may modulate only the affective-motivational dimension and leave the sensory-discriminative dimension relatively undisturbed.<ref name=M&C>{{cite book|last1=Melzack|first1=Ronald|author-link1=Ronald Melzack|last2=Casey|first2=Kenneth|author-link2=Kenneth L. Casey|editor-last=Kenshalo|editor-first=Dan|year=1968|chapter=Sensory, Motivational, and Central Control Determinants of Pain|title=The Skin Senses|publisher=Charles C Thomas|publication-place=Springfield, Illinois|url=https://www.researchgate.net/publication/233801589}}</ref> (p.&nbsp;432)

The paper ends with a call to action: "Pain can be treated not only by trying to cut down the sensory input by anesthetic block, surgical intervention and the like, but also by influencing the motivational-affective and cognitive factors as well."<ref name=M&C/> (p.&nbsp;435)

==Evolutionary and behavioral role==
Pain is part of the body's defense system, producing a [[Nervous system#Reflexes and other stimulus-response circuits|reflexive]] retraction from the painful stimulus, and tendencies to protect the affected body part while it heals, and avoid that harmful situation in the future.<ref name="Lynn1984">{{cite book|title=The neurobiology of pain: Symposium of the Northern Neurobiology Group, held at Leeds on 18 April 1983|vauthors=Lynn B|publisher=Manchester University Press|year=1984|isbn=978-0-7190-0996-9|veditors=Winlow W, Holden AV|location=Manchester|page=106|chapter=Cutaneous nociceptors|chapter-url=https://books.google.com/books?id=S7rnAAAAIAAJ&pg=PA106|access-date=3 February 2016|archive-date=30 March 2021|archive-url=https://web.archive.org/web/20210330014628/https://books.google.com/books?id=S7rnAAAAIAAJ&pg=PA106|url-status=live}}</ref><ref name= Bernston2008>{{cite book |vauthors=Bernston GG, Cacioppo JT |veditors=Gardner WL, Shah JY |title=Handbook of Motivation Science |publisher=The Guilford Press |location=New York |year=2007 |page=191 |isbn=978-1-59385-568-0 |chapter=The neuroevolution of motivation |chapter-url=https://books.google.com/books?id=iCxpZkZtDG8C&q=%22One+general+class+of+spinal+reflexes+consists+of+the+flexor+(pain)+withdrawal%22&pg=PT209 |access-date=18 November 2020 |archive-date=30 March 2021 |archive-url=https://web.archive.org/web/20210330014656/https://books.google.com/books?id=iCxpZkZtDG8C&q=%22One+general+class+of+spinal+reflexes+consists+of+the+flexor+%28pain%29+withdrawal%22&pg=PT209 |url-status=live }}</ref> It&nbsp;is&nbsp;an important part of animal life, vital to healthy [[survival]]. People with [[congenital insensitivity to pain]] have reduced [[life expectancy]].<ref name="pmid12583863"/>

In ''[[The Greatest Show on Earth: The Evidence for Evolution]]'', biologist [[Richard Dawkins]] addresses the question of why pain should have the quality of being painful. He describes the alternative as a mental raising of a "red flag". To argue why that red flag might be insufficient, Dawkins argues that drives must compete with one another within living beings. The most "fit" creature would be the one whose pains are well balanced. Those pains which mean certain death when ignored will become the most powerfully felt. The relative intensities of pain, then, may resemble the relative importance of that risk to our ancestors.{{efn|For example, lack of food, extreme cold, or serious injuries are felt as exceptionally painful, whereas minor damage is felt as mere discomfort.}} This resemblance will not be perfect, however, because natural selection can be a [[Argument from poor design|poor designer]]. This may have maladaptive results such as [[Supernormal stimulus|supernormal stimuli]].<ref name=Dawkins2009>{{cite book | vauthors = Dawkins R |year=2009 |title=The Greatest Show on Earth |url=https://archive.org/details/greatestshowonea00dawk |url-access=registration |publisher=Free Press |pages=[https://archive.org/details/greatestshowonea00dawk/page/392 392–395]|isbn=978-1-4165-9478-9 }}</ref>

Pain, however, does not only wave a "red flag" within living beings but may also act as a warning sign and a call for help to other living beings. Especially in humans who readily helped each other in case of sickness or injury throughout their evolutionary history, pain might be shaped by natural selection to be a credible and convincing signal of the need for relief, help, and care.<ref name = Steinkopf>{{cite journal |vauthors=Steinkopf L | date = June 2016 | title = An Evolutionary Perspective on Pain Communication | journal = Evolutionary Psychology | volume = 14 | issue = 2| page = 100 | article-number = 1474704916653964 | doi = 10.1177/1474704916653964 | doi-access = free | pmc = 10481100 }}</ref>

Idiopathic pain (pain that persists after the trauma or pathology has healed, or that arises without any apparent cause) may be an exception to the idea that pain is helpful to survival, although some [[psychodynamic]] psychologists argue that such pain is psychogenic, enlisted as a protective distraction to keep dangerous emotions unconscious.<ref name="Sarno-DividedMind">{{cite book | vauthors = Sarno JE |title=The divided mind: the epidemic of mindbody disorders | url = https://archive.org/details/dividedmindep00sarn | url-access = registration |publisher=ReganBooks |location=New York |year=2006 |isbn=978-0-06-117430-8}}</ref>

==Thresholds==
In pain science, thresholds are measured by gradually increasing the intensity of a stimulus in a procedure called [[quantitative sensory testing]] which involves such stimuli as [[electric current]], thermal (heat or cold), mechanical (pressure, touch, vibration), [[ischemia|ischemic]], or chemical stimuli applied to the subject to evoke a response.<ref name="Fillingim">{{cite journal | vauthors = Fillingim RB, Loeser JD, Baron R, Edwards RR | title = Assessment of Chronic Pain: Domains, Methods, and Mechanisms | journal = The Journal of Pain | volume = 17 | issue = 9 Suppl | pages = T10–20 | date = September 2016 | pmid = 27586827 | pmc = 5010652 | doi = 10.1016/j.jpain.2015.08.010 }}</ref> The "[[Threshold of pain|pain perception threshold]]" is the point at which the subject begins to feel pain, and the "pain threshold intensity" is the stimulus intensity at which the stimulus begins to hurt. The "[[pain tolerance]] threshold" is reached when the subject acts to stop the pain.<ref name=Fillingim/>

==Assessment== <!-- linked from [[Pain in babies]]-->
{{See also|Pain assessment|Pain scales|Pain ladder}}
A person's self-report is the most reliable measure of pain.<ref>{{cite book | vauthors = Amico D |title=Health & physical assessment in nursing |publisher=Pearson |location=Boston |year=2016 |page=173 |isbn=978-0-13-387640-6}}</ref><ref>{{cite book | vauthors = Taylor C |title= Fundamentals of nursing: the art and science of person-centered nursing care |publisher=Wolters Kluwer Health |location=Philadelphia |year=2015 |isbn=978-1-4511-8561-4 |page=241}}</ref><ref>{{cite book | vauthors = Venes D |title=Taber's cyclopedic medical dictionary |publisher=F.A. Davis |location=Philadelphia |year=2013 |isbn=978-0-8036-2977-6 |page=1716}}</ref> Some health care professionals may underestimate pain severity.<ref name= Prkachin2007>{{cite journal | vauthors = Prkachin KM, Solomon PE, Ross J | title = Underestimation of pain by health-care providers: towards a model of the process of inferring pain in others | journal = The Canadian Journal of Nursing Research | volume = 39 | issue = 2 | pages = 88–106 | date = June 2007 | pmid = 17679587 }}</ref> A definition of pain widely employed in nursing, emphasizing its subjective nature and the importance of believing patient reports, was introduced by [[Margo McCaffery]] in 1968: "Pain is whatever the experiencing person says it is, existing whenever he says it does".<ref>McCaffery M. (1968). ''Nursing practice theories related to cognition, bodily pain, and man-environment interactions''. Los Angeles: UCLA Students Store.<br />More recently, McCaffery defined pain as "whatever the experiencing person says it is, existing whenever the experiencing person says it does." {{cite book | vauthors = Pasero C, McCaffery M |title=Pain: clinical manual |publisher=Mosby |location=St. Louis |year=1999 |isbn=978-0-8151-5609-3}}</ref> To assess intensity, the patient may be asked to locate their pain on a scale of 0&nbsp;to&nbsp;10, with 0 being no pain at all, and 10 the worst pain they have ever felt. Quality can be established by having the patient complete the [[McGill Pain Questionnaire]] indicating which words best describe their pain.<ref name= Breivik2008/>

===Visual analogue scale===
{{Main|Visual analogue scale}}
The visual analogue scale is a common, reproducible tool in the assessment of pain and pain relief.<ref>{{cite journal | vauthors = Kelly AM | title = The minimum clinically significant difference in visual analogue scale pain score does not differ with severity of pain | journal = Emergency Medicine Journal | volume = 18 | issue = 3 | pages = 205–207 | date = May 2001 | pmid = 11354213 | pmc = 1725574 | doi = 10.1136/emj.18.3.205 }}</ref> The scale is a continuous line anchored by verbal descriptors, one for each extreme of pain where a higher score indicates greater pain intensity. It is usually 10&nbsp;cm in length with no intermediate descriptors as to avoid marking of scores around a preferred numeric value. When applied as a pain descriptor, these anchors are often 'no pain' and 'worst imaginable pain". Cut-offs for pain classification have been recommended as no pain (0–4mm), mild pain (5–44mm), moderate pain (45–74mm) and severe pain (75–100mm).<ref>{{cite journal | vauthors = Hawker GA, Mian S, Kendzerska T, French M | title = Measures of adult pain: Visual Analog Scale for Pain (VAS Pain), Numeric Rating Scale for Pain (NRS Pain), McGill Pain Questionnaire (MPQ), Short-Form McGill Pain Questionnaire (SF-MPQ), Chronic Pain Grade Scale (CPGS), Short Form-36 Bodily Pain Scale (SF-36 BPS), and Measure of Intermittent and Constant Osteoarthritis Pain (ICOAP) | journal = Arthritis Care & Research | volume = 63 | issue = S11 | pages = S240–252 | date = November 2011 | pmid = 22588748 | doi = 10.1002/acr.20543 }}</ref>{{check quotation}}

===Multidimensional pain inventory===
The Multidimensional Pain Inventory (MPI) is a questionnaire designed to assess the [[psychosocial]] state of a person with chronic pain. Combining the MPI characterization of the person with their [[#Classification|IASP five-category pain profile]] is recommended for deriving the most useful case description.<ref name = Turk&Okifuji2001/>

===Assessment in non-verbal people===
{{See also|Pain and dementia|Pain in babies}}
[[Nonverbal communication|Non-verbal]] people cannot use words to tell others that they are experiencing pain. However, they may be able to communicate through other means, such as blinking, pointing, or nodding.<ref name=":1">{{Cite book|title=Medical-surgical nursing: Assessment and management of clinical problems| vauthors = Lewis SM, Bucher L, Heitkemper MM, Harding M |publisher= Elsevier |year=2017 |isbn=978-0-323-32852-4 |edition=10th|location=St. Louis, Missouri|pages=126|oclc=944472408}}</ref>

With a non-communicative person, observation becomes critical, and specific behaviors can be monitored as pain indicators. Behaviors such as facial grimacing and guarding (trying to protect part of the body from being bumped or touched) indicate pain, as well as an increase or decrease in vocalizations, changes in routine behavior patterns and mental status changes. Patients experiencing pain may exhibit withdrawn [[social behavior]] and possibly experience a [[Anorexia (symptom)|decreased appetite]] and decreased nutritional intake. A change in condition that deviates from baseline, such as moaning with movement or when manipulating a body part, and limited [[range of motion]] are also potential pain indicators. In patients who possess language but are incapable of expressing themselves effectively, such as those with dementia, an increase in confusion or display of aggressive behaviors or agitation may signal that discomfort exists, and further assessment is necessary. Changes in behavior may be noticed by caregivers who are familiar with the person's normal behavior.<ref name=":1" />

[[Pain in babies|Infants do feel pain]], but lack the language needed to report it, and so communicate distress by crying. A non-verbal pain assessment should be conducted involving the parents, who will notice changes in the infant which may not be obvious to the health care provider. [[Preterm birth|Pre-term babies]] are more sensitive to painful stimuli than those carried to full term.<ref name= Jarvis2004>{{cite book | vauthors = Jarvis C |title=Physical examination & health assessment |publisher=Elsevier Saunders |location=St. Louis, Mo |year=2007 |pages=180–192 |isbn=978-1-4557-2810-7}}</ref>

Another approach, when pain is suspected, is to give the person treatment for pain, and then watch to see whether the suspected indicators of pain subside.<ref name=":1" />

===Other reporting barriers===
The way in which one experiences and responds to pain is related to sociocultural characteristics, such as gender, ethnicity, and age.<ref>{{cite journal | vauthors = Encandela JA | title = Social science and the study of pain since Zborowski: a need for a new agenda | journal = Social Science & Medicine | volume = 36 | issue = 6 | pages = 783–791 | date = March 1993 | pmid = 8480223 | doi = 10.1016/0277-9536(93)90039-7 }}</ref><ref>Zborowski M. ''People in Pain''. 1969, San Francisco, CA:Josey-Bass{{ISBN?}}{{page needed|date=January 2023}}</ref> An aging adult may not respond to pain in the same way that a younger person might. Their ability to recognize pain may be blunted by illness or the use of [[prescription drug|medication]]. Depression may also keep older adult from reporting they are in pain. Decline in [[self-care]] may also indicate the older adult is experiencing pain. They may be reluctant to report pain because they do not want to be perceived as weak, or may feel it is impolite or shameful to complain, or they may feel the pain is a form of deserved punishment.<ref>{{cite journal | vauthors = Encandela JA |year=1997 |title=Social Construction of pain and aging: Individual artfulness within interpretive structures |journal= Symbolic Interaction|volume=20 |issue=3 |pages=251–273 |doi=10.1525/si.1997.20.3.251}}</ref><ref>{{cite book | vauthors = Lawhorne L, Passerini J | date = 1999 | title = Chronic Pain Management in the Long Term Care Setting: Clinical Practice Guidelines. | location = Baltimore, Maryland | publisher = American Medical Directors Association | pages = 1–27 }}</ref>

Cultural barriers may also affect the likelihood of reporting pain. Patients may feel that certain treatments go against their religious beliefs. They may not report pain because they feel it is a sign that death is near. Many people fear the stigma of addiction, and avoid pain treatment so as not to be prescribed potentially addicting drugs. Many Asians do not want to lose respect in society by admitting they are in pain and need help, believing the pain should be borne in silence, while other cultures feel they should report pain immediately to receive immediate relief.<ref name= Jarvis2004/>

Gender can also be a perceived factor in reporting pain. [[Gender differences]] can be the result of social and cultural expectations, with, in some cultures, women expected to be more emotional and show pain, and men to be more stoic.<ref name= Jarvis2004/> As a result, female pain may be at a higher risk of being stigmatized, leading to less urgent treatment of women based on social expectations of their ability to accurately report it.<ref>{{cite news | vauthors = Epstein R |date=19 March 2018 |title=When Doctors Don't Listen to Women |url=https://www.nytimes.com/2018/03/19/books/review/abby-norman-ask-me-about-my-uterus.html |work=The New York Times |access-date=20 July 2019 |archive-date=9 May 2019 |archive-url=https://web.archive.org/web/20190509110006/https://www.nytimes.com/2018/03/19/books/review/abby-norman-ask-me-about-my-uterus.html |url-status=live }}</ref> This has been postulated to lead to extended emergency room wait times for women and frequent dismissal of their ability to accurately report pain.<ref>{{cite news | vauthors = Fasslet J |date=15 October 2015 |title=How Doctors Take Women's Pain Less Seriously |url=https://www.theatlantic.com/health/archive/2015/10/emergency-room-wait-times-sexism/410515/ |work=The Atlantic |access-date=20 July 2019 |archive-date=17 July 2019 |archive-url= https://web.archive.org/web/20190717161732/https://www.theatlantic.com/health/archive/2015/10/emergency-room-wait-times-sexism/410515/ |url-status=live }}</ref><ref>{{cite news |author=<!--Staff writer(s); no by-line.--> |title=Stories of Misunderstanding Women's Pain |url=https://www.theatlantic.com/notes/all/2015/10/stories-of-misunderstood-womens-pain/411793/ |work=The Atlantic |date=15 March 2016 |access-date=20 July 2019 |archive-date=15 April 2019 |archive-url=https://web.archive.org/web/20190415114017/https://www.theatlantic.com/notes/all/2015/10/stories-of-misunderstood-womens-pain/411793/ |url-status=live }}</ref>

===Diagnostic aid===
Pain is a symptom of many medical conditions. Knowing the time of onset, location, intensity, pattern of occurrence (continuous, intermittent, etc.), exacerbating and relieving factors, and quality (burning, sharp, etc.) of the pain will help the examining physician to accurately diagnose the problem. For example, chest pain described as extreme heaviness may indicate [[myocardial infarction]], while chest pain described as tearing may indicate [[aortic dissection]].<ref name="pmid9786377">{{cite journal | vauthors = Panju AA, Hemmelgarn BR, Guyatt GH, Simel DL | title = The rational clinical examination. Is this patient having a myocardial infarction? | journal = JAMA | volume = 280 | issue = 14 | pages = 1256–1263 | date = October 1998 | pmid = 9786377 | doi = 10.1001/jama.280.14.1256 }}</ref><ref name="pmid1020750">{{cite journal | vauthors = Slater EE, DeSanctis RW | title = The clinical recognition of dissecting aortic aneurysm | journal = The American Journal of Medicine | volume = 60 | issue = 5 | pages = 625–633 | date = May 1976 | pmid = 1020750 | doi = 10.1016/0002-9343(76)90496-4 }}</ref>

===Physiological measurement===
[[Functional magnetic resonance imaging]] brain scanning has been used to measure pain, and correlates well with self-reported pain.<ref>{{cite journal | vauthors = Brown JE, Chatterjee N, Younger J, Mackey S | title = Towards a physiology-based measure of pain: patterns of human brain activity distinguish painful from non-painful thermal stimulation | journal = PLOS ONE | volume = 6 | issue = 9 | article-number = e24124 | date = September 2011 | pmid = 21931652 | pmc = 3172232 | doi = 10.1371/journal.pone.0024124 | bibcode = 2011PLoSO...624124B | doi-access = free }}</ref><ref>{{cite web |url=https://www.medicalnewstoday.com/articles/234450.php |title=Tool That Measures Pain Objectively Under Way |work=Medical News Today |date=15 September 2011 | vauthors = Paddock C |access-date=25 September 2017 |url-status=live |archive-url=https://web.archive.org/web/20170925230621/https://www.medicalnewstoday.com/articles/234450.php |archive-date=25 September 2017 }}</ref><ref>{{Cite news |quote=Editorial|url=https://www.reuters.com/article/us-pain-diagnostic-idUSTRE78C81920110913 |title=Feeling pain? The computer can tell |date=13 September 2011 |newspaper=Reuters |access-date=25 September 2017 |url-status=live |archive-url=https://web.archive.org/web/20150617221847/https://www.reuters.com/article/2011/09/13/us-pain-diagnostic-idUSTRE78C81920110913 |archive-date=17 June 2015 }}</ref>

==Mechanisms==
=== Nociceptive ===
{{Main|Nociception}}
[[File:Nociceptive pain.jpg|thumb|288x288px|Mechanism of nociceptive pain]]

Nociceptive pain is caused by stimulation of [[Sensory nervous system|sensory nerve fibers]] that respond to stimuli approaching or exceeding harmful intensity ([[nociceptor]]s), and may be classified according to the mode of noxious stimulation. The most common categories are "thermal" (e.g. heat or cold), "mechanical" (e.g. crushing, tearing, shearing, etc.) and "chemical" (e.g. [[iodine]] in a cut or chemicals released during [[inflammation]]). Some nociceptors respond to more than one of these modalities and are consequently designated polymodal.

Nociceptive pain may also be classed according to the site of origin and divided into "visceral", "deep somatic" and "superficial somatic" pain. [[Viscus|Visceral structures]] (e.g., the heart, liver and intestines) are highly sensitive to stretch, [[ischemia]] and [[inflammation]], but relatively insensitive to other stimuli that normally evoke pain in other structures, such as burning and cutting. [[Visceral pain]] is diffuse, difficult to locate and often [[referred pain|referred]] to a distant, usually superficial, structure. It may be accompanied by nausea and vomiting and may be described as sickening, deep, squeezing, and dull.<ref name = Urch>{{cite book | vauthors = Urch CE, Suzuki R |chapter=Pathophysiology of somatic, visceral, and neuropathic cancer pain |editor=Sykes N, Bennett MI & Yuan C-S |title=Clinical pain management: Cancer pain |edition=2d |isbn=978-0-340-94007-5 |publisher=Hodder Arnold |location=London |pages=3–12|date=26 September 2008 }}</ref> ''Deep somatic'' pain is initiated by stimulation of nociceptors in ligaments, tendons, bones, blood vessels, [[fascia]]e and muscles, and is dull, aching, poorly-localized pain. Examples include [[sprain]]s and broken bones. ''Superficial somatic'' pain is initiated by activation of nociceptors in the skin or other superficial tissue, and is sharp, well-defined and clearly located. Examples of injuries that produce superficial somatic pain include minor wounds and minor (first degree) burns.<ref name="isbn0-443-05683-8">{{cite book |vauthors=Coda BA, Bonica JJ |veditors=Panswick CC, Main CJ |title=Pain management: an interdisciplinary approach |publisher=Churchill Livingstone |location=Edinburgh |year=2000 |isbn=978-0-443-05683-3 |chapter=General considerations of acute pain |chapter-url-access=registration |chapter-url=https://archive.org/details/painmanagementin0000main }}</ref>

=== Neuropathic ===
{{Main|Neuropathic pain}}

Neuropathic pain is caused by damage or disease affecting any part of the [[nervous system]] involved in bodily feelings (the [[somatosensory system]]).<ref name="Treede">{{cite journal | vauthors = Treede RD, Jensen TS, Campbell JN, Cruccu G, Dostrovsky JO, Griffin JW, Hansson P, Hughes R, Nurmikko T, Serra J | title = Neuropathic pain: redefinition and a grading system for clinical and research purposes | journal = Neurology | volume = 70 | issue = 18 | pages = 1630–1635 | date = April 2008 | pmid = 18003941 | doi = 10.1212/01.wnl.0000282763.29778.59 | hdl = 11573/97043 | s2cid = 30172528 }}</ref> Neuropathic pain may be divided into peripheral, [[central pain syndrome|central]], or mixed (peripheral and central) neuropathic pain. [[Peripheral nervous system|Peripheral]] neuropathic pain is often described as "burning", "tingling", "electrical", "stabbing", or "pins and needles".<ref>{{cite journal | vauthors = Paice JA | title = Mechanisms and management of neuropathic pain in cancer | journal = The Journal of Supportive Oncology | volume = 1 | issue = 2 | pages = 107–120 | year = 2003 | pmid = 15352654 | url = https://www.supportiveoncology.net/journal/articles/0102107.pdf | archive-url = https://web.archive.org/web/20100107161021/https://www.supportiveoncology.net/journal/articles/0102107.pdf | archive-date = 7 January 2010 | access-date = 8 January 2010 }}</ref> Bumping the "[[funny bone]]" elicits acute peripheral neuropathic pain.

Some manifestations of neuropathic pain include: traumatic neuropathy, [[tic douloureux]], painful [[diabetic neuropathy]], and [[postherpetic neuralgia]].<ref>{{cite journal | vauthors = Campbell JN, Meyer RA | title = Mechanisms of neuropathic pain | journal = Neuron | volume = 52 | issue = 1 | pages = 77–92 | date = October 2006 | pmid = 17015228 | pmc = 1810425 | doi = 10.1016/j.neuron.2006.09.021 }}</ref>

=== Nociplastic ===
{{Main|Nociplastic pain}}

Nociplastic pain is pain characterized by a changed [[nociception]] (but without evidence of real or threatened tissue damage, or without disease or damage in the [[somatosensory system]]).<ref name="Mind-Body Therapies for Opioid-Trea"/>

=== Psychogenic ===
{{Main|Psychogenic pain}}
Psychogenic pain, also called ''psychalgia'' or ''somatoform pain'', is pain caused, increased or prolonged by mental, emotional or behavioral factors.<ref name="Cleveland Clinic"/> Headaches, back pain and stomach pain are sometimes diagnosed as psychogenic.<ref name="Cleveland Clinic">{{cite web |url=https://my.clevelandclinic.org/services/Pain_Management/hic_Psychogenic_Pain.aspx |title=Psychogenic Pain |publisher=[[Cleveland Clinic]] |access-date=25 September 2017 |url-status=live |archive-url=https://archive.wikiwix.com/cache/20110714011822/https://my.clevelandclinic.org/services/Pain_Management/hic_Psychogenic_Pain.aspx |archive-date=14 July 2011 }}</ref> Those affected are often stigmatized, because both medical professionals and the general public tend to think that pain from a psychological source is not "real". However, specialists consider that it is no less actual or hurtful than pain from any other source.<ref name=IASP_definitions>[https://web.archive.org/web/20080512061229/https://www.iasp-pain.org/AM/Template.cfm?Section=General_Resource_Links&Template=%2FCM%2FHTMLDisplay.cfm&ContentID=3058#Pain "International Association for the Study of Pain | Pain Definitions".]. Retrieved 12 October 2010.</ref>

People with [[chronic pain|long-term pain]] frequently display psychological disturbance, with elevated scores on the [[Minnesota Multiphasic Personality Inventory]] scales of [[hysteria]], depression and [[hypochondriasis]] (the "[[neurotic triad]]"). Some investigators have argued that it is this neuroticism that causes acute pain to turn chronic, but clinical evidence points in the other direction, to chronic pain causing [[neuroticism]]. When long-term pain is relieved by therapeutic intervention, scores on the neurotic triad and [[anxiety]] fall, often to normal levels. [[Self-esteem]], often low in chronic pain patients, also shows improvement once pain has resolved.<ref name = "The challenge of pain"/>{{rp|31–32}}

==Management==
{{Main|Pain management}}
{{Further|Pain management in children|Pain management during childbirth}}

Pain can be treated through a variety of methods. The most appropriate method depends upon the situation. Management of [[chronic pain]] can be difficult and may require the coordinated efforts of a [[pain management]] team, which typically includes [[medical practitioner]]s, clinical pharmacists, [[clinical psychologist]]s, [[physiotherapist]]s, [[occupational therapist]]s, [[physician assistant]]s, and [[nurse practitioner]]s.<ref>{{cite book|title=Pain management: A practical guide for clinicians|vauthors=Thienhaus O, Cole BE|date=2002|publisher=American Academy of Pain Management|isbn=978-0-8493-2262-4|veditors=Weiner RS|page=29|chapter=The classification of pain}}
* {{cite book|url=https://archive.org/details/painmanagementin0000main|title=Pain management: an interdisciplinary approach|vauthors=Main CJ, Spanswick CC|date=2000|publisher=Churchill Livingstone|isbn=978-0-443-05683-3|quote=Pain management: an interdisciplinary approach.|url-access=registration}}</ref>

Inadequate treatment of pain is widespread throughout surgical wards, [[intensive care units]], and accident and [[emergency departments]], in [[General practitioner|general practice]], in the management of all forms of chronic pain including cancer pain, and in [[End-of-life care|end of life care]].<ref>{{cite journal | vauthors = Brown AK, Christo PJ, Wu CL | title = Strategies for postoperative pain management | journal = Best Practice & Research. Clinical Anaesthesiology | volume = 18 | issue = 4 | pages = 703–717 | date = December 2004 | pmid = 15460554 | doi = 10.1016/j.bpa.2004.05.004 }}</ref><ref>{{cite journal | vauthors = Cullen L, Greiner J, Titler MG | title = Pain management in the culture of critical care | journal = Critical Care Nursing Clinics of North America | volume = 13 | issue = 2 | pages = 151–166 | date = June 2001 | pmid = 11866399 | doi = 10.1016/S0899-5885(18)30046-7 }}</ref><ref>{{cite journal | vauthors = Rupp T, Delaney KA | title = Inadequate analgesia in emergency medicine | journal = Annals of Emergency Medicine | volume = 43 | issue = 4 | pages = 494–503 | date = April 2004 | pmid = 15039693 | doi = 10.1016/j.annemergmed.2003.11.019 }}</ref><ref>{{cite journal | vauthors = Smith GF, Toonen TR | title = Primary care of the patient with cancer | journal = American Family Physician | volume = 75 | issue = 8 | pages = 1207–1214 | date = April 2007 | pmid = 17477104 }}</ref><ref>{{cite journal | vauthors = Jacobson PL, Mann JD | title = Evolving role of the neurologist in the diagnosis and treatment of chronic noncancer pain | journal = Mayo Clinic Proceedings | volume = 78 | issue = 1 | pages = 80–84 | date = January 2003 | pmid = 12528880 | doi = 10.4065/78.1.80 }}</ref><ref>{{cite journal | vauthors = Deandrea S, Montanari M, Moja L, Apolone G | title = Prevalence of undertreatment in cancer pain. A review of published literature | journal = Annals of Oncology | volume = 19 | issue = 12 | pages = 1985–1991 | date = December 2008 | pmid = 18632721 | pmc = 2733110 | doi = 10.1093/annonc/mdn419 }}</ref><ref>{{cite journal | vauthors = Perron V, Schonwetter RS | title = Assessment and management of pain in palliative care patients | journal = Cancer Control | volume = 8 | issue = 1 | pages = 15–24 | year = 2001 | pmid = 11176032 | doi = 10.1177/107327480100800103 | doi-access = free }}</ref> This neglect extends to all ages, from newborns to [[medically frail]] elderly.<ref>{{cite book |vauthors=Selbst SM, Fein JA |veditors=Henretig FM, Fleisher GR, Ludwig S |title=Textbook of pediatric emergency medicine |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |year=2006 |isbn=978-1-60547-159-4 |chapter=Sedation and analgesia |chapter-url=https://books.google.com/books?id=oA7qSOvYZxUC&pg=PA63 |access-date=3 February 2016 |archive-date=11 June 2016 |archive-url=https://web.archive.org/web/20160611170847/https://books.google.com/books?id=oA7qSOvYZxUC&pg=PA63 |url-status=live }}</ref><ref>{{cite journal | vauthors = Cleeland CS | title = Undertreatment of cancer pain in elderly patients | journal = JAMA | volume = 279 | issue = 23 | pages = 1914–1915 | date = June 1998 | pmid = 9634265 | doi = 10.1001/jama.279.23.1914 }}</ref> In the US, [[African Americans|African]] and [[Hispanic and Latino Americans|Hispanic Americans]] are more likely than others to suffer unnecessarily while in the care of a physician;<ref>{{cite journal | vauthors = Bonham VL | title = Race, ethnicity, and pain treatment: striving to understand the causes and solutions to the disparities in pain treatment | journal = The Journal of Law, Medicine & Ethics | volume = 29 | issue = 1 | pages = 52–68 | year = 2001 | pmid = 11521272 | doi = 10.1111/j.1748-720X.2001.tb00039.x | s2cid = 18257031 | url = https://www.painandthelaw.org/aslme_content/29-1/bonham.pdf | archive-url = https://web.archive.org/web/20110719132135/https://www.painandthelaw.org/aslme_content/29-1/bonham.pdf | archive-date = 19 July 2011 | access-date = 7 March 2022 }}</ref><ref>{{cite journal | vauthors = Green CR, Anderson KO, Baker TA, Campbell LC, Decker S, Fillingim RB, Kalauokalani DA, Kaloukalani DA, Lasch KE, Myers C, Tait RC, Todd KH, Vallerand AH | title = The unequal burden of pain: confronting racial and ethnic disparities in pain | journal = Pain Medicine | volume = 4 | issue = 3 | pages = 277–294 | date = September 2003 | pmid = 12974827 | doi = 10.1046/j.1526-4637.2003.03034.x | hdl = 2027.42/73822 | url = https://deepblue.lib.umich.edu/bitstream/2027.42/73822/1/j.1526-4637.2003.03034.x.pdf | access-date = 2 September 2019 | archive-date = 30 March 2021 | archive-url = https://web.archive.org/web/20210330014611/https://deepblue.lib.umich.edu/bitstream/handle/2027.42/73822/j.1526-4637.2003.03034.x.pdf;jsessionid=9D282F272A80BFE500C544F4D9C57617?sequence=1 | url-status = live | doi-access = free }}</ref> and women's pain is more likely to be undertreated than men's.<ref name="pmid11521267">{{cite journal | vauthors = Hoffmann DE, Tarzian AJ | title = The girl who cried pain: a bias against women in the treatment of pain | journal = The Journal of Law, Medicine & Ethics | volume = 29 | issue = 1 | pages = 13–27 | year = 2001 | pmid = 11521267 | doi = 10.1111/j.1748-720X.2001.tb00037.x | s2cid = 219952180 | url = https://digitalcommons.law.umaryland.edu/cgi/viewcontent.cgi?article=1144&context=fac_pubs | access-date = 11 July 2019 | archive-date = 1 November 2019 | archive-url = https://web.archive.org/web/20191101132951/https://digitalcommons.law.umaryland.edu/cgi/viewcontent.cgi?article=1144&context=fac_pubs | url-status = live | url-access = subscription }}</ref>

The [[International Association for the Study of Pain]] advocates that the relief of pain should be recognized as a [[human right]], that chronic pain should be considered a disease in its own right, and that [[pain medicine]] should have the full status of a [[Specialty (medicine)|medical specialty]].<ref>{{cite web | author = Delegates to the International Pain Summit of the International Association for the Study of Pain | date = 2010 | url = https://www.iasp-pain.org/AM/Template.cfm?Section=Declaration_of_MontrandNum233_al | title = Declaration of Montreal | archive-url = https://web.archive.org/web/20110513203221/https://www.iasp-pain.org/AM/Template.cfm?Section=Declaration_of_MontrandNum233_al | archive-date = 13 May 2011 | access-date = 7 March 2022 }}</ref> It is a specialty only in China and Australia at this time.<ref name="isbn0-7817-7388-1">{{cite book | vauthors = Horlocker TT, Cousins MJ, Bridenbaugh PO, Carr DL |title=Cousins and Bridenbaugh's Neural Blockade in Clinical Anesthesia and Pain Medicine |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |year=2008 |isbn=978-0-7817-7388-1}}</ref> Elsewhere, pain medicine is a subspecialty under disciplines such as [[anesthesiology]], [[physiatry]], [[neurology]], [[palliative medicine]] and [[psychiatry]].<ref>{{cite web | url = https://www.abms.org/Who_We_Help/Consumers/About_Physician_Specialties/physical.aspx | title = Physical Medicine and Rehabilitation | archive-url = https://web.archive.org/web/20080516091310/https://www.abms.org/Who_We_Help/Consumers/About_Physician_Specialties/physical.aspx | archive-date = 16 May 2008 | access-date = 7 March 2022 }}</ref> In 2011, [[Human Rights Watch]] alerted that tens of millions of people worldwide are still denied access to inexpensive medications for severe pain.<ref>{{cite web |author=Human Rights Watch |author-link=Human Rights Watch |url=https://www.hrw.org/news/2011/06/02/global-tens-millions-face-death-agony |title=Tens of Millions Face Death in Agony |year=2011 |access-date=26 August 2013 |url-status=live |archive-url=https://web.archive.org/web/20130901232156/https://www.hrw.org/news/2011/06/02/global-tens-millions-face-death-agony |archive-date=1 September 2013 }}</ref>

===Medication===
Acute pain is usually managed with medications such as [[analgesic]]s and [[anesthetic]]s.<ref name="researchgate.net">{{cite journal | vauthors = Mallinson TE |title=A review of ketorolac as a prehospital analgesic |journal=Journal of Paramedic Practice |date=2017 |volume=9 |issue=12 |pages=522–526 |url=https://www.researchgate.net/publication/321640488 |access-date=2 June 2018 |language=en |doi=10.12968/jpar.2017.9.12.522 |doi-access=free |archive-date=5 June 2018 |archive-url=https://web.archive.org/web/20180605033254/https://www.researchgate.net/publication/321640488_A_review_of_ketorolac_as_a_prehospital_analgesic |url-status=live }}</ref> [[Caffeine]] when added to pain medications such as [[ibuprofen]], may provide some additional benefit.<ref>{{cite journal | vauthors = Derry CJ, Derry S, Moore RA | title = Caffeine as an analgesic adjuvant for acute pain in adults | journal = The Cochrane Database of Systematic Reviews | volume = 12 | issue = 12 | article-number = CD009281 | date = December 2014 | pmid = 25502052 | pmc = 6485702 | doi = 10.1002/14651858.CD009281.pub3 }}</ref><ref>{{cite journal | vauthors = Derry S, Wiffen PJ, Moore RA | title = Single dose oral ibuprofen plus caffeine for acute postoperative pain in adults | journal = The Cochrane Database of Systematic Reviews | issue = 7 | article-number = CD011509 | date = July 2015 | volume = 2019 | pmid = 26171993 | pmc = 6481458 | doi = 10.1002/14651858.CD011509.pub2 }}</ref> [[Ketamine]] can be used instead of opioids for short-term pain.<ref>{{cite journal | vauthors = Karlow N, Schlaepfer CH, Stoll CR, Doering M, Carpenter CR, Colditz GA, Motov S, Miller J, Schwarz ES | display-authors = 6 | title = A Systematic Review and Meta-analysis of Ketamine as an Alternative to Opioids for Acute Pain in the Emergency Department | journal = Academic Emergency Medicine | volume = 25 | issue = 10 | pages = 1086–1097 | date = October 2018 | pmid = 30019434 | doi = 10.1111/acem.13502 | doi-access = free }}</ref> Pain medications can cause paradoxical side effects, such as [[opioid-induced hyperalgesia]] (severe generalized pain caused by long-term opioid use).<ref>{{cite journal | vauthors = Higgins C, Smith BH, Matthews K | title = Evidence of opioid-induced hyperalgesia in clinical populations after chronic opioid exposure: a systematic review and meta-analysis | journal = British Journal of Anaesthesia | volume = 122 | issue = 6 | pages = e114–e126 | date = June 2019 | pmid = 30915985 | doi = 10.1016/j.bja.2018.09.019 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Fishbain DA, Pulikal A | title = Does Opioid Tapering in Chronic Pain Patients Result in Improved Pain or Same Pain vs Increased Pain at Taper Completion? A Structured Evidence-Based Systematic Review | journal = Pain Medicine | volume = 20 | issue = 11 | pages = 2179–2197 | date = November 2019 | pmid = 30597076 | doi = 10.1093/pm/pny231 }}</ref>

{{anchor|Oral sugar}}

Sugar ([[sucrose]]) when taken by mouth reduces [[Pain in babies|pain in newborn babies]] undergoing some medical procedures (a [[Incision and drainage|lancing]] of the heel, [[venipuncture]], and [[intramuscular injections]]). Sugar does not remove pain from [[circumcision]], and it is unknown if sugar reduces pain for other procedures.<ref name="StevensYamada2016">{{cite journal | vauthors = Stevens B, Yamada J, Ohlsson A, Haliburton S, Shorkey A | title = Sucrose for analgesia in newborn infants undergoing painful procedures | journal = The Cochrane Database of Systematic Reviews | volume = 7 | article-number = CD001069 | date = July 2016 | issue = 2 | pmid = 27420164 | pmc = 6457867 | doi = 10.1002/14651858.CD001069.pub5 }}</ref> Sugar did not affect pain-related [[EEG|electrical activity]] in the brains of newborns one second after the heel lance procedure.<ref>{{cite journal | vauthors = Lasky RE, van Drongelen W | title = Is sucrose an effective analgesic for newborn babies? | journal = Lancet | volume = 376 | issue = 9748 | pages = 1201–1203 | date = October 2010 | pmid = 20817245 | doi = 10.1016/S0140-6736(10)61358-X | s2cid = 18724497 }}</ref> Sweet liquid by mouth moderately reduces the rate and duration of crying caused by immunization injection in children between one and twelve months of age.<ref>{{cite journal | vauthors = Harrison D, Stevens B, Bueno M, Yamada J, Adams-Webber T, Beyene J, Ohlsson A | title = Efficacy of sweet solutions for analgesia in infants between 1 and 12 months of age: a systematic review | journal = Archives of Disease in Childhood | volume = 95 | issue = 6 | pages = 406–413 | date = June 2010 | pmid = 20463370 | doi = 10.1136/adc.2009.174227 | doi-access = free }}</ref>

===Psychological===
Individuals with more [[social support]] experience less cancer pain, take less pain medication, report less labor pain and are less likely to use [[Epidural administration|epidural anesthesia]] during childbirth, or suffer from chest pain after [[coronary artery bypass surgery]].<ref name="Eisenberger_2005" />

[[Suggestion]] can significantly affect pain intensity. About 35% of people report marked relief after receiving a [[Saline (medicine)|saline]] injection they believed to be [[morphine]]. This [[placebo]] effect is more pronounced in people who are prone to anxiety, and so anxiety reduction may account for some of the effect, but it does not account for all of it. Placebos are more effective for intense pain than mild pain; and they produce progressively weaker effects with repeated administration.<ref name = "The challenge of pain"/>{{rp|26–28}} It is possible for many with chronic pain to become so absorbed in an activity or entertainment that the pain is no longer felt, or is greatly diminished.<ref name = "The challenge of pain"/>{{rp|22–23}}

A number of meta-analyses have found [[clinical hypnosis]] to be effective in controlling pain associated with diagnostic and surgical procedures in both adults and children, as well as pain associated with cancer and childbirth.<ref name="pmid18714889">{{cite journal | vauthors = Wark DM | title = What we can do with hypnosis: a brief note | journal = The American Journal of Clinical Hypnosis | volume = 51 | issue = 1 | pages = 29–36 | date = July 2008 | pmid = 18714889 | doi = 10.1080/00029157.2008.10401640 | s2cid = 12240662 }}</ref> A 2007 review of 13 studies found evidence for the efficacy of hypnosis in the reduction of chronic pain under some conditions, though the number of patients enrolled in the studies was low, raising issues related to the statistical power to detect group differences, and most lacked credible controls for placebo or expectation. The authors concluded that "although the findings provide support for the general applicability of hypnosis in the treatment of chronic pain, considerably more research will be needed to fully determine the effects of hypnosis for different chronic-pain conditions."<ref name= Elkins2007>{{cite journal | vauthors = Elkins G, Jensen MP, Patterson DR | title = Hypnotherapy for the management of chronic pain | journal = The International Journal of Clinical and Experimental Hypnosis | volume = 55 | issue = 3 | pages = 275–287 | date = July 2007 | pmid = 17558718 | pmc = 2752362 | doi = 10.1080/00207140701338621 }}</ref>

===Alternative medicine===
An analysis of the 13 highest quality studies of pain treatment with [[acupuncture]], published in January 2009, concluded there was little difference in the effect of real, fake and no acupuncture.<ref>{{cite journal | vauthors = Madsen MV, Gøtzsche PC, Hróbjartsson A | title = Acupuncture treatment for pain: systematic review of randomised clinical trials with acupuncture, placebo acupuncture, and no acupuncture groups | journal = BMJ | volume = 338 | article-number = a3115 | date = January 2009 | pmid = 19174438 | pmc = 2769056 | doi = 10.1136/bmj.a3115 }}</ref> However, more recent reviews have found some benefit.<ref>{{cite journal | vauthors = Chiu HY, Hsieh YJ, Tsai PS | title = Systematic review and meta-analysis of acupuncture to reduce cancer-related pain | journal = European Journal of Cancer Care | volume = 26 | issue = 2 | article-number = e12457 | date = March 2017 | pmid = 26853524 | doi = 10.1111/ecc.12457 | s2cid = 20096639 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Chang SC, Hsu CH, Hsu CK, Yang SS, Chang SJ | title = The efficacy of acupuncture in managing patients with chronic prostatitis/chronic pelvic pain syndrome: A systemic review and meta-analysis | journal = Neurourology and Urodynamics | volume = 36 | issue = 2 | pages = 474–481 | date = February 2017 | pmid = 26741647 | doi = 10.1002/nau.22958 | s2cid = 46827576 }}</ref><ref>{{cite journal | vauthors = Ji M, Wang X, Chen M, Shen Y, Zhang X, Yang J | title = The Efficacy of Acupuncture for the Treatment of Sciatica: A Systematic Review and Meta-Analysis | journal = Evidence-Based Complementary and Alternative Medicine | volume = 2015 | article-number = 192808 | date = 2015 | pmid = 26425130 | pmc = 4575738 | doi = 10.1155/2015/192808 | doi-access = free }}</ref>

Additionally, there is tentative evidence for a few herbal medicines.<ref>{{cite journal | vauthors = Gagnier JJ, Oltean H, van Tulder MW, Berman BM, Bombardier C, Robbins CB | title = Herbal Medicine for Low Back Pain: A Cochrane Review | journal = Spine | volume = 41 | issue = 2 | pages = 116–133 | date = January 2016 | pmid = 26630428 | doi = 10.1097/BRS.0000000000001310 }}</ref>

For chronic (long-term) [[Low back pain|lower back pain]], [[spinal manipulation]] produces tiny, [[Clinical significance|clinically insignificant]], short-term improvements in pain and function, compared with [[sham therapy]] and other interventions.<ref name="Rubinstein CD008880">{{cite journal | vauthors = Rubinstein SM, Terwee CB, Assendelft WJ, de Boer MR, van Tulder MW | title = Spinal manipulative therapy for acute low-back pain | journal = The Cochrane Database of Systematic Reviews | issue = 9 | article-number = CD008880 | date = September 2012 | volume = 2012 | pmid = 22972127 | pmc = 6885055 | doi = 10.1002/14651858.CD008880.pub2 }}</ref> Spinal manipulation produces the same outcome as other treatments, such as general practitioner care, pain-relief drugs, physical therapy, and exercise, for acute (short-term) lower back pain.<ref name="Rubinstein CD008880"/>

There has been some interest in the relationship between [[vitamin D]] and pain, but the evidence so far from [[Clinical trial|controlled trials]] for such a relationship, other than in [[osteomalacia]], is inconclusive.<ref name= Straube>{{cite journal | vauthors = Straube S, Andrew Moore R, Derry S, McQuay HJ | title = Vitamin D and chronic pain | journal = Pain | volume = 141 | issue = 1–2 | pages = 10–13 | date = January 2009 | pmid = 19084336 | doi = 10.1016/j.pain.2008.11.010 | s2cid = 17244398 }}</ref>

The International Association for the Study of Pain (IASP) says that due to a lack of evidence from high quality research, it does not endorse the general use of cannabinoids to treat pain.<ref>{{cite web|access-date=2024-05-10|language=en|publisher=iasp-pain|title=IASP Position Statement on the Use of Cannabinoids to Treat Pain|url=https://www.iasp-pain.org/publications/iasp-news/iasp-position-statement-on-the-use-of-cannabinoids-to-treat-pain/|archive-date=10 May 2024|archive-url=https://web.archive.org/web/20240510095147/https://www.iasp-pain.org/publications/iasp-news/iasp-position-statement-on-the-use-of-cannabinoids-to-treat-pain/|url-status=live}}</ref>

==Epidemiology==
Pain is the main reason for visiting an [[emergency department]] in more than 50% of cases,<ref>{{cite journal | vauthors = Cordell WH, Keene KK, Giles BK, Jones JB, Jones JH, Brizendine EJ | title = The high prevalence of pain in emergency medical care | journal = The American Journal of Emergency Medicine | volume = 20 | issue = 3 | pages = 165–169 | date = May 2002 | pmid = 11992334 | doi = 10.1053/ajem.2002.32643 }}</ref> and is present in 30% of family practice visits.<ref name="pmid12160512">{{cite journal | vauthors = Hasselström J, Liu-Palmgren J, Rasjö-Wrååk G | title = Prevalence of pain in general practice | journal = European Journal of Pain | volume = 6 | issue = 5 | pages = 375–385 | year = 2002 | pmid = 12160512 | doi = 10.1016/S1090-3801(02)00025-3 | s2cid = 798849 }}</ref> Several [[epidemiological]] studies have reported widely varying prevalence rates for chronic pain, ranging from 12 to 80% of the population.<ref name="pmid20358856">{{cite journal | vauthors = Abu-Saad Huijer H | title = Chronic pain: a review | journal = Le Journal Medical Libanais. The Lebanese Medical Journal | volume = 58 | issue = 1 | pages = 21–27 | year = 2010 | pmid = 20358856 }}</ref> It becomes more common as people approach death. A study of 4,703 patients found that 26% had pain in the last two years of life, increasing to 46% in the last month.<ref name=Death2010>{{cite journal | vauthors = Smith AK, Cenzer IS, Knight SJ, Puntillo KA, Widera E, Williams BA, Boscardin WJ, Covinsky KE | title = The epidemiology of pain during the last 2 years of life | journal = Annals of Internal Medicine | volume = 153 | issue = 9 | pages = 563–569 | date = November 2010 | pmid = 21041575 | pmc = 3150170 | doi = 10.7326/0003-4819-153-9-201011020-00005 }}</ref>

A survey of 6,636 children (0–18 years of age) found that, of the 5,424 respondents, 54% had experienced pain in the preceding three months. A quarter reported having experienced recurrent or continuous pain for three months or more, and a third of these reported frequent and intense pain. The intensity of chronic pain was higher for girls, and girls' reports of chronic pain increased markedly between ages 12 and 14.<ref name="pmid10863045">{{cite journal | vauthors = Perquin CW, Hazebroek-Kampschreur AA, Hunfeld JA, Bohnen AM, van Suijlekom-Smit LW, Passchier J, van der Wouden JC | title = Pain in children and adolescents: a common experience | journal = Pain | volume = 87 | issue = 1 | pages = 51–58 | date = July 2000 | pmid = 10863045 | doi = 10.1016/S0304-3959(00)00269-4 | s2cid = 9813003 }}</ref>

==Society and culture==
[[File:Lamani v kole.jpg|thumb|The [[breaking wheel]] was a torture method used for [[Capital punishment#Public execution|public execution]] by breaking the bones of a criminal or [[Club (weapon)|bludgeoning]] them to death.]]
[[File:TUCANDEIRA RITUAL - panoramio.jpg|thumb|The [[Mawé people]] of Brazil intentionally use [[bullet ant]] stings as a [[rite of passage]] into manhood.]]
Physical pain is a universal experience, and a strong motivator of [[human behaviour|human]] and [[animal behavior]]. As such, physical pain is used politically in relation to various issues such as [[pain management]] policy, [[Drug policy|drug control]], [[animal rights]] or [[animal welfare]], [[torture]], and [[pain compliance]]. The deliberate infliction of pain and the medical management of pain are both important aspects of [[biopower]], a concept that encompasses the "set of mechanisms through which the basic biological features of the human species became the object of a political strategy".<ref>{{Cite book| vauthors = Foucault M |title=Security, Territory, Population: Lectures at the College de France, 1977–78|publisher=Palgrave Macmillan|year=2007|page=1}}</ref>

In various contexts, the deliberate infliction of pain in the form of [[corporal punishment]] is used as retribution for an offence, for the purpose of disciplining or reforming a wrongdoer, or to deter attitudes or behaviour deemed unacceptable. In Western societies, the intentional infliction of severe pain (torture) was principally used to extract confession prior to its abolition in the latter part of the 19th century. Torture as a means to punish the [[Citizenship|citizen]] has been reserved for offences posing a severe threat to the social fabric (for example, [[treason]]).<ref name="fall-rise-of-torture">{{cite journal | vauthors = Einolf C | date=2007 | title=The Fall and Rise of Torture: A Comparative and Historical Analysis | jstor=20453071 | journal=Social Theory | volume=25 | issue=2 | pages=101–121 | doi=10.1111/j.1467-9558.2007.00300.x | s2cid=53345959 | url=https://works.bepress.com/cgi/viewcontent.cgi?article=1008&context=christopher_einolf }}</ref>

The administration of torture on bodies othered by the cultural narrative, those observed as not 'full members of society' <ref name="fall-rise-of-torture" />{{rp|101–121[AD1] }} met a resurgence in the 20th century, possibly due to the heightened warfare.<ref name="fall-rise-of-torture" />{{rp|101–121 [AD2] }}

Many cultures use painful ritual practices as a catalyst for psychological transformation.<ref name="ritual-experience">{{cite journal | vauthors = Morinis A | date=1985 | title=The ritual experience: pain and the transformation of consciousness in ordeals of initiation | jstor=639985 | journal=Ethos | volume=13 | issue=2 | pages=150–174 | doi=10.1525/eth.1985.13.2.02a00040 |doi-access=free}}</ref> The use of pain to transition to a 'cleansed and purified' state is seen in religious [[self-flagellation]] practices (particularly those of [[Self-flagellation#Christianity|Christianity]] and [[Self-flagellation#Islam|Islam]]), or personal [[catharsis]] in [[Suspension (body modification)|neo-primitive body suspension]] experiences.<ref name="flesh-journeys">{{cite journal | vauthors = Atkinson M, Young K | date=2001 | title=Flesh journeys: neo primitives and the contemporary rediscovery of radical body modification | journal=Deviant Behavior | volume=22 | issue=2 | pages=117–146 | doi=10.1080/016396201750065018 | s2cid=146525156 }}</ref>

Beliefs about pain play an important role in sporting cultures. Pain may be viewed positively, exemplified by the 'no pain, no gain' attitude, with pain seen as an essential part of training. Sporting culture tends to normalise experiences of pain and injury and celebrate athletes who 'play hurt'.<ref>{{Cite book| veditors = Loland S, Skirstad B, Waddington I |title=Pain and injury in sport: Social and ethical analysis |publisher=Routledge |year=2006|isbn=978-0-415-35704-3 |location=London and New York |pages=17–20}}</ref>

Pain has psychological, social, and physical dimensions, and is greatly influenced by cultural factors.<ref name="how-culture-pain-experience">{{cite journal | vauthors = Narayan MC | title = Culture's effects on pain assessment and management | journal = The American Journal of Nursing | volume = 110 | issue = 4 | pages = 38–47 | date = April 2010 | pmid = 20335689 | doi = 10.1097/01.NAJ.0000370157.33223.6d | doi-access = free }}</ref>

==Non-humans==

===Animals===
{{Main|Pain in animals|Pain in invertebrates}}

[[René Descartes]] argued that animals lack consciousness and therefore do not experience pain and suffering in the way that humans do.<ref name="nuffield45">Working party of the Nuffield Council on Bioethics (2005). [https://web.archive.org/web/20080625033250/https://www.nuffieldbioethics.org/fileLibrary/pdf/RIA_Report_FINAL-opt.pdf "The ethics of research involving animals. London: Nuffield Council on Bioethics."] {{ISBN|978-1904384106}}. Archived from the original on 25 June 2008. Retrieved 12 January 2010.</ref> [[Bernard Rollin]] of [[Colorado State University]], the principal author of two U.S. federal laws regulating pain relief for animals,{{efn|Rollin drafted the 1985 Health Research Extension Act and an [[animal welfare]] amendment to the 1985 Food Security Act.<ref>{{cite journal | vauthors = Rollin BE | title = Animal research: a moral science. Talking Point on the use of animals in scientific research | journal = EMBO Reports | volume = 8 | issue = 6 | pages = 521–525 | date = June 2007 | pmid = 17545990 | pmc = 2002540 | doi = 10.1038/sj.embor.7400996 }}</ref>}} wrote that researchers remained unsure into the 1980s as to whether animals experience pain, and that veterinarians trained in the U.S. before 1989 were simply taught to ignore animal pain.<ref name="Rollin117">{{cite book | vauthors = Rollin B | date = 1989 | title = The Unheeded Cry: Animal Consciousness, Animal Pain, and Science | location = New York | publisher = Oxford University Press | pages = 117–118 }} cited in {{cite book | vauthors = Carbone L | title = What animals want: expertise and advocacy in laboratory animal welfare policy. | publisher = Oxford University Press | location = US| date = 2004 | page = 150 }}</ref><ref name="pmid14658059">{{cite journal | vauthors = Griffin DR, Speck GB | title = New evidence of animal consciousness | journal = Animal Cognition | volume = 7 | issue = 1 | pages = 5–18 | date = January 2004 | pmid = 14658059 | doi = 10.1007/s10071-003-0203-x | s2cid = 8650837 }}</ref> The ability of invertebrate species of animals, such as insects, to feel pain and suffering is unclear.<ref name="Sherwin, 2001">{{cite journal | vauthors = Sherwin CM | title = Can invertebrates suffer? Or, how robust is argument-by-analogy? | journal = Animal Welfare | date = February 2001 | volume = 10 | issue = 1 | pages = 103–118 | doi = 10.1017/S0962728600023551 | s2cid = 54126137 | url = https://www.ingentaconnect.com/contentone/ufaw/aw/2001/00000010/a00101s1/art00010;jsessionid=1dtup2ob3at3b.x-ic-live-02 | access-date = 22 December 2021 | archive-date = 7 March 2022 | archive-url = https://web.archive.org/web/20220307174545/https://www.ingentaconnect.com/contentone/ufaw/aw/2001/00000010/a00101s1/art00010;jsessionid=1dtup2ob3at3b.x-ic-live-02 | url-status = live | url-access = subscription }}</ref><ref>{{cite journal | vauthors = Lockwood JA |year=1987 |title=The Moral Standing of Insects and the Ethics of Extinction |jstor=3495093 |journal=The Florida Entomologist |volume=70 |issue=1 |pages=70–89 |doi=10.2307/3495093|doi-access=free }}</ref><ref>{{cite journal | vauthors = DeGrazia D, Rowan A | title = Pain, suffering, and anxiety in animals and humans | journal = Theoretical Medicine | volume = 12 | issue = 3 | pages = 193–211 | date = September 1991 | pmid = 1754965 | doi = 10.1007/BF00489606 | s2cid = 34920699 }}</ref>

Specialists believe that all vertebrates can feel pain, and that certain invertebrates, like the octopus, may also.<ref name="Sherwin, 2001" /><ref>{{cite web | url = https://sencanada.ca/content/sen/committee/372/lega/witn/shelly-e.htm | title = Do Invertebrates Feel Pain? | archive-url = https://web.archive.org/web/20100106084119/https://sencanada.ca/content/sen/committee/372/lega/witn/shelly-e.htm | archive-date=6 January 2010 | work = The Senate Standing Committee on Legal and Constitutional Affairs | publisher = The [[Parliament of Canada]] | access-date = 11 June 2008 }}</ref><ref>{{cite journal | vauthors = Smith JA |year=1991 |title=A Question of Pain in Invertebrates |url=https://www.abolitionist.com/darwinian-life/invertebrate-pain.html |journal=Institute for Laboratory Animal Research Journal |volume=33 |pages=1–2 |url-status=live |archive-url=https://web.archive.org/web/20111008212237/https://www.abolitionist.com/darwinian-life/invertebrate-pain.html |archive-date=8 October 2011 }}</ref> The presence of pain in animals is unknown, but can be inferred through physical and behavioral reactions,<ref name="pmid7715946">{{cite journal | vauthors = Abbott FV, Franklin KB, Westbrook FR | title = The formalin test: scoring properties of the first and second phases of the pain response in rats | journal = Pain | volume = 60 | issue = 1 | pages = 91–102 | date = January 1995 | pmid = 7715946 | doi = 10.1016/0304-3959(94)00095-V | s2cid = 35448280 }}</ref> such as paw withdrawal from various noxious mechanical stimuli in rodents.<ref>{{cite journal | vauthors = Jones JM, Foster W, Twomey CR, Burdge J, Ahmed OM, Pereira TD, Wojick JA, Corder G, Plotkin JB, Abdus-Saboor I | display-authors = 6 | title = A machine-vision approach for automated pain measurement at millisecond timescales | journal = eLife | volume = 9 | article-number = e57258 | date = August 2020 | pmid = 32758355 | pmc = 7434442 | doi = 10.7554/eLife.57258 | doi-access = free }}</ref>

===Plants===
While [[plants]], as living beings, can perceive and communicate physical stimuli and damage, they do not feel pain simply because of the lack of any pain receptors, nerves, or a brain,<ref name="EncyBrit"/> and, by extension, a lack of consciousness.<ref>{{cite journal| last1 = Draguhn| first1 = Andreas | last2 = Mallatt| first2 = Jon M. | last3 = Robinson| first3 = David G. | title = Anesthetics and plants: no pain, no brain, and therefore no consciousness| journal = Protoplasma| volume = 258| issue = 2| pages = 239–248| publisher = Springer | date = 2021| language = | jstor = | issn = | doi = 10.1007/s00709-020-01550-9| pmid = 32880005 | pmc = 7907021 | bibcode = 2021Prpls.258..239D | id = 32880005| mr = | zbl = | jfm = }}</ref> Many plants are known to perceive and respond to mechanical stimuli at a cellular level, and some plants such as the [[venus flytrap]] or [[Mimosa pudica|touch-me-not]], are known for their "obvious sensory abilities".<ref name="EncyBrit"/> Nevertheless, no member of the plant kingdom does feel pain not withstanding their abilities to respond to sunlight, gravity, wind, and any external stimuli such as insect bites since they lack any nervous system. The primary reason for this is that, unlike the members of the [[Animal|animal kingdom]] whose evolutionary successes and failures are shaped by suffering, the evolution of plants is simply shaped by life and death.<ref name="EncyBrit">{{cite web
| url = https://www.britannica.com/story/do-plants-feel-pain
| title = Do Plants Feel Pain?
| last = Petruzzello
| first = Melissa
| date = 2016
| website = Encyclopedia Britannica
| access-date = 8 January 2023
| quote = Given that plants do not have pain receptors, nerves, or a brain, they do not feel pain as we members of the animal kingdom understand it. Uprooting a carrot or trimming a hedge is not a form of botanical torture, and you can bite into that apple without worry.
| archive-date = 5 September 2023
| archive-url = https://web.archive.org/web/20230905171721/https://www.britannica.com/story/do-plants-feel-pain
| url-status = live
}}</ref>

== See also ==
* [[Feeling]], a perceptual state of conscious experience.
* [[Hedonic adaptation]], the tendency to quickly return to a relatively stable level of happiness despite major positive or negative events
* [[Pain (philosophy)]], the branch of philosophy concerned with suffering and physical pain
* [[Pain and suffering]], the legal term for the physical and emotional stress caused from an injury
* [[Suffering]], an experience of unpleasantness or aversion, possibly associated with the perception of harm or threat of harm in an individual.

== Explanatory notes ==
{{notelist}}

== References ==
{{Reflist}}

==Further reading==
* {{cite book | vauthors = Casey K |date=2019 |title=Chasing Pain: The Search for a Neurobiological Mechanism |location=New York |publisher=Oxford University Press |isbn=978-0-19-088023-1 }}
* Allison Parshall, "Pain Language: The sound of 'ow' transcends borders", ''[[Scientific American]]'', vol. 332, no. 2 (February 2025), pp. 16–18.   "Many [[language]]s have an [[interjection]] word for expressing pain. [Katarzyna Pisanski ''et al.'', writing in the ''[[Journal of the Acoustical Society of America]]'', have] found that pain interjections tend to contain the [[vowel]] sound 'ah' (written as [a] in the [[International Phonetic Alphabet]]) and letter combinations that incorporate it, such as 'ow' and 'ai.' These patterns may point back to the origins of human language itself." (p. 16.) "Researchers are continually discovering cases of [[Artistic symbol|symbolism]], or sound [[iconicity]], in which a word's intrinsic nature has some connection to its meaning. These cases run counter to decades of [[linguistic theory]], which had regarded language as fundamentally arbitrary... [Many words [[onomatopoeia|onomatopoeically]] imitate a sound. Also] there's the [[Bouba/kiki effect|'bouba-kiki' effect]], whereby people from varying cultures are more likely to associate the nonsense word 'bouba' with a rounded shape and 'kiki' with a spiked one.... [S]omehow we all have a ''feeling'' about this,' says Aleksandra Ćwiek... [She and her colleagues have] show[n] that people associate the [[Trill consonant|trilled]] 'R' sound with roughness and the 'L' sound with smoothness. [[Mark Dingemanse]]... in 2013 found [that] the conversational 'Huh?' and similar words in other languages may be universal." (p. 18.)

== External links ==
{{Commons category}}
{{Wikiquote}}
{{wikibooks|Sensory Systems|Physiology of Pain}}
{{wikibooks|Internal Medicine|Pain}}
* [https://plato.stanford.edu/entries/pain/ "Pain"], ''[[Stanford Encyclopedia of Philosophy]]''

{{Medical resources
|  ICD11          = {{ICD11|MG30}} (chronic), {{ICD11|MG31}} (acute), {{ICD11|8E43.00}} (phantom pain)
|  ICD10          = {{ICD10|R52}}
|  ICD9           = {{ICD9|338}}
|  MedlinePlus    = 002164
|  DiseasesDB     = 9503
|  MeshID         = D010146
}}
{{Emotion-footer}}
{{Neuroscience}}
{{Pain}}
{{Somatosensory system}}
{{Sensation and perception}}
{{Authority control}}

[[Category:Pain| ]]
[[Category:Acute pain]]
[[Category:Nociception]]
[[Category:Sensory systems]]
[[Category:Suffering]]
[[Category:Symptoms and signs]]