View source for Edema

{{Short description|Accumulation of excess fluid in tissue}}
{{cs1 config|name-list-style=vanc}}
{{Redirect|Dropsy||dropsy (disambiguation)|and|edema (plants)}}
{{Infobox medical condition
| name           = Edema
| image          = Combinpedal.jpg
| caption        = "Pitting" edema
| field          = [[Cardiology]], [[nephrology]]
| synonyms        = Oedema, œdema, fluid retention, water retention, dropsy, hydropsy
| pronounce       = {{IPAc-en|ᵻ|ˈ|d|iː|m|ə}}
| symptoms        = Skin which feels tight, area may feel heavy<ref name=IQ2016/>
| complications   =
| onset           = Sudden or gradual<ref name=Mer2019/>
| duration        =
| causes          = [[Chronic venous insufficiency|Venous insufficiency]], [[heart failure]], [[kidney problems]], [[hypoalbuminemia|low protein levels]], [[liver problems]], [[deep vein thrombosis]], [[lymphedema]]<ref name= IQ2016 /><ref name=Mer2019 />
| risks           =
| types           = Generalized, localized<ref name=Mer2019/>
| diagnosis       = Based on a [[physical exam]]<ref name= FP2019 />
| differential    =
| prevention      =
| treatment       = Based on cause<ref name=Mer2019/>
| medication      =
| prognosis       =
| frequency       =
| deaths          =
}}

<!-- Definition and symptoms -->
'''Edema''' ([[American English]]), also spelled '''oedema''' ([[Commonwealth English]]), and also known as '''fluid retention''', '''swelling''', '''dropsy''' and '''hydropsy''', is the build-up of fluid in the body's [[tissue (biology)|tissue]].<ref name= IQ2016>{{cite book |title=Causes and signs of edema |date=2016 |publisher=Institute for Quality and Efficiency in Health Care (IQWiG) |url= https://www.ncbi.nlm.nih.gov/books/NBK279409/}}</ref><ref>{{Cite book |last=Creason |first=Charlotte |url=https://books.google.com/books?id=YISsnVIEJgkC&dq=%22a+type+of+swelling%22+edema&pg=PA29 |title=Stedman's Medical Terminology: Steps to Success in Medical Language |date=2010-11-04 |publisher=Lippincott Williams & Wilkins |isbn=978-1-58255-816-5 |language=en}}</ref> Most commonly, the legs or arms are affected.<ref name=IQ2016/> Symptoms may include skin that feels tight, the area feeling heavy, and joint stiffness.<ref name=IQ2016/> Other symptoms depend on the underlying cause.<ref name= Mer2019 />

<!-- Cause and diagnosis -->
Causes may include [[Chronic venous insufficiency|venous insufficiency]], [[heart failure]], [[kidney problems]], [[hypoalbuminemia|low protein levels]], [[liver problems]], [[deep vein thrombosis]], infections, [[kwashiorkor]], [[angioedema]], certain medications, and [[lymphedema]].<ref name=IQ2016/><ref name=Mer2019>{{cite web |title=Edema - Cardiovascular Disorders |url= https://www.merckmanuals.com/professional/cardiovascular-disorders/symptoms-of-cardiovascular-disorders/edema |website=Merck Manuals Professional Edition |access-date=8 December 2019}}</ref> It may also occur in immobile patients (stroke, spinal cord injury, aging), or with temporary immobility such as prolonged sitting or standing, and during [[menstruation]] or [[pregnancy]].<ref name=IQ2016/> The condition is more concerning if it starts suddenly, or pain or shortness of breath is present.<ref name=Mer2019/>

<!-- Treatment and culture -->
Treatment depends on the underlying cause.<ref name= Mer2019/> If the underlying mechanism involves [[Hypernatremia|sodium retention]], decreased salt intake and a [[diuretic]] may be used.<ref name=Mer2019/> Elevating the legs and [[support stockings]] may be useful for edema of the legs.<ref name= FP2019/> Older people are more commonly affected.<ref name= FP2019>{{cite web |title=Edema: Causes, Symptoms, Diagnosis & Treatment |url= https://familydoctor.org/condition/edema/?adfree=true |website= Family doctor |access-date= 23 December 2019}}</ref> The word is from the [[Ancient Greek]] {{lang|grc|οἴδημα}} ''oídēma'' meaning 'swelling'.<ref>{{cite web |last1= Liddell |first1=Henry | work = A Greek-English Lexicon | title = οἴδ-ημα |url= https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Doi%29%2Fdhma | publisher = Tufts |access-date= 8 December 2019}}</ref>

==Signs and symptoms==
{{More citations needed section|date=December 2024}}

===Specific area===
An edema will occur in specific organs as part of inflammation, [[Tendonopathy|tendinitis]] or [[pancreatitis]]. Certain organs develop edema through tissue specific mechanisms. Examples of edema in specific organs:
* [[Peripheral edema]] ("dependent" edema of legs) is extracellular fluid accumulation in the lower extremities caused by the effects of gravity, and occurs when fluid pools in the lower parts of the body, including the feet, legs, or hands.<ref name="goyal">{{Citation |last=Goyal |first=Amandeep |title=Peripheral Edema |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK554452/ |access-date=2025-07-06 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32119339 |last2=Singh |first2=Baltej |last3=Afzal |first3=Muriam}}</ref> This often occurs in immobile people, such as paraplegics or quadriplegics, pregnant women, or in otherwise healthy people due to [[hypervolemia]] or maintaining a standing or seated posture for an extended time.<ref name=goyal/> It can occur due to diminished venous return of blood to the heart due to congestive heart failure or [[pulmonary hypertension]].<ref name=goyal/> It can also occur in people with increased hydrostatic venous pressure or decreased oncotic venous pressure, due to obstruction of lymphatic or venous vessels draining the lower extremity. Certain drugs (for example, amlodipine) can cause edema of the feet.
* [[Cerebral edema]] is extracellular fluid accumulation in the brain.<ref name="IQ2016" /> It can occur in toxic or abnormal metabolic states and conditions such as systemic lupus or reduced oxygen at high altitudes. It causes drowsiness or loss of consciousness, leading to [[brain herniation]] and death.
* [[Pulmonary edema]] occurs when the pressure in blood vessels in the lung is raised because of obstruction to the removal of blood via the pulmonary veins. This is usually due to failure of the left ventricle of the heart. It can also occur in altitude sickness or on inhalation of toxic chemicals. Pulmonary edema produces shortness of breath. [[Pleural effusion]]s may occur when fluid also accumulates in the [[pleural]] cavity.<ref>{{Citation |last=Malek |first=Ryan |title=Pulmonary Edema |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK557611/ |access-date=2025-07-06 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32491543 |last2=Soufi |first2=Shadi}}</ref>
* Edema may also be found in the cornea of the eye with [[glaucoma]], severe [[conjunctivitis]], [[keratitis]], or after surgery. Affected people may perceive coloured haloes around bright lights.
* Edema surrounding the eyes is called [[periorbital edema]] (puffy eyes) . The periorbital tissues are most noticeably swollen immediately after waking, perhaps as a result of the gravitational redistribution of fluid in the horizontal position.
* Common appearances of [[cutaneous]] edema are observed with [[mosquito]] bites, [[spider]] bites, bee stings ([[wheal and flare]]), and skin contact with certain plants such as [[poison ivy]] or [[western poison oak]],<ref>{{cite web |first=C. Michael |last=Hogan |year=2008 |url=http://globaltwitcher.auderis.se/artspec_information.asp?thingid=82914 |title=Western poison-oak: Toxicodendron diversilobum |archive-url=https://web.archive.org/web/20090721044257/http://globaltwitcher.auderis.se/artspec_information.asp?thingid=82914 |archive-date=July 21, 2009  |website=GlobalTwitcher |editor-first=Nicklas |editor-last=Strömberg}}</ref> the latter of which are termed ''[[contact dermatitis]]''.
* Another cutaneous form of edema is [[myxedema]], which is caused by increased deposition of [[connective tissue]]. In myxedema (and a variety of other rarer conditions) edema is caused by an increased tendency of the tissue to hold water within its extracellular space. In myxedema, this is due to  an increase in hydrophilic carbohydrate-rich molecules (perhaps mostly [[hyaluronin]]) deposited in the tissue matrix. Edema forms more easily in dependent areas in the elderly (sitting in chairs at home or on aeroplanes) and this is not well understood. Estrogens alter body weight in part through changes in tissue water content. There may be a variety of poorly understood situations in which transfer of water from tissue matrix to lymphatics is impaired because of changes in the hydrophilicity of the tissue or failure of the 'wicking' function of terminal lymphatic capillaries.
* Myoedema is localized mounding of muscle tissue due to percussive pressure, such as flicking the relaxed muscle with the forefinger and thumb.{{medcn|date=July 2025}} It produces a mound, visible, firm and non-tender at the point of tactile stimulus approximately 1–2 seconds after stimulus, subsiding back to normal after 5–10 seconds. It is a sign in hypothyroid myopathy, such as [[Hoffmann syndrome]].<ref>{{Cite journal |last1=Vignesh |first1=G |last2=Balachandran |first2=Karthik |last3=Kamalanathan |first3=Sadishkumar |last4=Hamide |first4=Abdoul |date=2013 |title=Myoedema: A clinical pointer to hypothyroid myopathy |journal=Indian Journal of Endocrinology and Metabolism |volume=17 |issue=2 |pages=352 |doi=10.4103/2230-8210.109672 |issn=2230-8210 |pmc=3683223 |pmid=23776921 |doi-access=free }}</ref>
* In [[lymphedema]], abnormal removal of interstitial fluid is caused by failure of the [[lymphatic system]].{{medcn|date=July 2025}} This is most commonly due to a failure of normal pumping action of muscles due to immobility—most strikingly in conditions such as multiple sclerosis or paraplegia. Or it may be due to obstruction by a [[cancer]] or by enlarged [[lymph nodes]]; or to destruction of lymph vessels or nodes by [[radiotherapy]]; or from infiltration of the lymphatic system by infection (such as [[Podoconiosis|elephantiasis]]). It has been suggested that the edema that occurs following use of aspirin-like cyclo-oxygenase inhibitors, such as ibuprofen or indomethacin, may be due to inhibition of lymph heart action.

{{Gallery
|height=200
|width =150
|whitebg=no
|style = margin-top:1em;
|Image:Geschwollener menschlicher Fuß.JPG|Foot two weeks post-surgery.
|Image:MyParonychia.jpg|The [[distal phalanx]] of the right finger exhibits edema due to [[acute paronychia]].
|Image:SeverePedalEdema.jpg|Severe edema in the legs and feet.
}}

=== Generalized ===
A rise in [[hydrostatic pressure]] occurs in cardiac failure. A fall in osmotic pressure occurs in [[nephrotic syndrome]] and [[liver failure]].<ref name="pmid8790586">{{cite journal |last= Renkin |first=EM | title = Cellular aspects of transvascular exchange: a 40-year perspective | journal = Microcirculation | volume = 1 | issue = 3 | pages = 157–67 | year = 1994 | pmid = 8790586 | doi = 10.3109/10739689409148270 | s2cid = 28046134 }}</ref>

Causes of edema that are generalized to the whole body can cause edema in multiple organs and peripherally. For example, severe heart failure can cause [[pulmonary edema]], pleural effusions, [[ascites]] and [[peripheral edema]]. Such severe systemic edema is called [[anasarca]]. In rare cases, a [[parvovirus B19]] infection may cause generalized edemas.<ref name="pmid23472922">{{cite journal |vauthors=Wiggli B, Imhof E, Meier CA, Laifer G | title = Water, water, everywhere. Acute parvovirus B19 infection | journal = Lancet | volume = 381 | issue = 9868 | pages = 776 | year = 2013 | pmid = 23472922 | doi = 10.1016/S0140-6736(12)61894-7 | s2cid = 19300719 }}</ref>

Although a low plasma [[oncotic pressure]] is widely cited for the edema of nephrotic syndrome, most physicians note that the edema may occur before there is any significant protein in the urine ([[proteinuria]]) or fall in plasma protein level. Most forms of nephrotic syndrome are due to biochemical and structural changes in the basement membrane of capillaries in the kidney glomeruli, and these changes occur, if to a lesser degree, in the vessels of most other tissues of the body. Thus the resulting increase in permeability that leads to protein in the urine can explain the edema if all other vessels are more permeable as well.<ref name="pmid9185099">{{cite journal |vauthors=Palmer BF, Alpern RJ | title = Pathogenesis of edema formation in the nephrotic syndrome | journal = Kidney Int. Suppl. | volume = 59 | pages = S21–7 | year = 1997 | pmid = 9185099 }}</ref>

As well as the previously mentioned conditions, edemas often occur during the late stages of pregnancy in some women. This is more common with those of a history of pulmonary problems or poor circulation also being intensified if arthritis is already present in that particular woman. Women who already have arthritic problems most often have to seek medical help for pain caused from over-reactive swelling. Edemas that occur during pregnancy are usually found in the lower part of the leg, usually from the calf down.

[[Hydrops fetalis]] is a condition in a baby characterized by an accumulation of fluid in at least two body compartments.

==Cause==
=== Heart ===
The pumping force of the [[human heart|heart]] should help to keep a normal pressure within the [[blood vessel]]s. But if the heart begins to fail (a condition known as [[congestive heart failure]]) the pressure changes can cause very severe water retention. In this condition water retention is mostly visible in the [[human leg|leg]]s, feet and [[ankle]]s, but water also collects in the [[lungs]], where it causes a chronic [[cough]]. This condition is usually treated with [[diuretics]]; otherwise, the water retention may cause breathing problems and additional stress on the heart.<ref name=":0">{{Cite journal|last1=Casu|first1=Gavino|last2=Merella|first2=Pierluigi|date=July 2015|title=Diuretic Therapy in Heart Failure – Current Approaches|journal=European Cardiology Review|volume=10|issue=1|pages=42–47|doi=10.15420/ecr.2015.10.01.42|issn=1758-3756|pmc=6159465|pmid=30310422}}</ref>

=== Kidneys ===
Another cause of severe water retention is [[kidney failure]], where the [[kidneys]] are no longer able to filter fluid out of the [[blood]] and turn it into [[urine]]. [[Kidney disease]] often starts with [[inflammation]], for instance in the case of diseases such as [[nephrotic syndrome]] or [[Systemic lupus erythematosus|lupus]]. This type of water retention is usually visible in the form of swollen [[human leg|leg]]s and [[ankle]]s.<ref name=":3">{{Cite web |title=Edema - Symptoms and causes |url=https://www.mayoclinic.org/diseases-conditions/edema/symptoms-causes/syc-20366493 |access-date=2022-07-19 |website=Mayo Clinic |language=en}}</ref>

=== Liver ===
[[Cirrhosis]] (scarring) of the liver is a common cause of edema in the legs and abdominal cavity.<ref name=":3" />

=== Veins ===
Phlebetic lymphedema (or phlebolymphedema) is seen in untreated [[chronic venous insufficiency]] and is the most common type of edema (approx. 90%).<ref name=":1">{{Cite web |last1=Publishing |first1=Licorn |last2=Guiboles |date=2009-11-24 |title=The causes of edema in chronic venous insufficiency |url=https://www.phlebolymphology.org/the-causes-of-edema-in-chronic-venous/ |access-date=2023-09-01 |website=Servier - Phlebolymphology |language=en-US}}</ref> It is a combination venous/lymphatic disorder that originates in defective "leaky" veins that allows the blood to back flow ([[Chronic venous insufficiency|venous reflux]]), slowing the return of the blood to the heart ([[venous stasis]]). The venous pressure in the legs changes dramatically while standing compared to lying down. How much pressure there is depends on the person's height, in the average adult person, it is 8 mm Hg while lying down and 100 mm Hg while standing.<ref name=":2">{{Cite journal |last=Farrow |first=Wade |date=2010 |title=Phlebolymphedema-a common underdiagnosed and undertreated problem in the wound care clinic |journal=The Journal of the American College of Certified Wound Specialists |volume=2 |issue=1 |pages=14–23 |doi=10.1016/j.jcws.2010.04.004 |issn=1876-4983 |pmc=3601853 |pmid=24527138}}</ref>

In venous insufficiency, venous stasis results in abnormally high venous pressure (venous hypertension) and greater permeability of blood capillaries (capillary hyperpermeability), to drain the blood through the lymphatic system. The lymphatic system slowly removes excess fluid and proteins from the veins in the lower legs towards the upper body; however, as it is not as efficient as an unimpaired circulatory system, swelling (edema) is visible, particularly in the ankles and lower leg. The chronic increased fluid in the lymphatic system and capillary hyperpermeability causes an inflammatory response which leads to tissue fibrosis of both veins and lymphatic system, opening of arteriovenous shunts, all of which then worsens the condition in a vicious cycle.<ref name=":1" /><ref name=":2" />

=== Others ===
Swollen [[human leg|leg]]s, feet and [[ankle]]s are common in late [[pregnancy]]. The problem is partly caused by the weight of the [[uterus]] on the major [[vein]]s of the [[human pelvis|pelvis]]. It usually clears up after delivery of the baby, and is mostly not a cause for concern,<ref>{{cite web |url=http://www.merck.com/mmpe/sec18/ch259/ch259e.html |first1=R. Phillips  |last1=Heine |first2=Geeta K. |last2=Swamy |title=Lower-Extremity Edema During Late Pregnancy |work=[[The Merck Manual]] |access-date=9 August 2017}}</ref> though it should always be reported to a doctor.

Lack of exercise is another common cause of water retention in the legs. Exercise helps the leg [[vein]]s work against [[gravity]] to return [[blood]] to the [[human heart|heart]]. If [[blood]] travels too slowly and starts to pool in the [[human leg|leg]] [[vein]]s, the pressure can force too much fluid out of the [[human leg|leg]] [[capillary|capillaries]] into the tissue spaces. The [[capillary|capillaries]] may break, leaving small blood marks under the [[human skin|skin]]. The [[vein]]s themselves can become swollen, painful and distorted – a condition known as [[varicose vein]]s.

Causes  of bilateral pedal edema:
(after exclusion of cardiac, renal, heart, liver and thyroid disorders, malnutrition or malabsorption).
*Drugs like CCBs, gabapentin, pregabalin, NSAIDs, steroids, IL-6 inhibitors (e.g., tocilizumab).
*Chronic leg vein insufficiency (duplex ultrasound of leg veins - often noncontributory).
*Reduced mobility (geriatric patients/ occupational/ prolonged standing or sitting in same position)> reduced calf muscle activity>dependent edema/ gravitational edema
*IVC obstruction/ other causes of venous stasis
*Capillary leakage: acute endothelial dysfunction, sepsis, dengue, systemic capillary leakage syndrome (SCLS) (e.g., MGUS) (associated with hypotension; 3rd space accumulation of fluid).
*Inflammatory edema: vasculitis/ arthritis (even OA - may have mild inflammation)/ dermatomyositis/panniculitis
* Vasomotor dysregulation like sympathetic denervation in diabetes, spinal cord injury,  double hemiplegia, paraplegia,  chronic stress related ( sympathetic activity> vasoconstriction>venous stasis; increased cortisol).
*Heat edema- in patients returning from cold climate
* Early lymphatic dysfunction including obesity (also RAAS)
* Other endocrine- Cushing/Conn/PMS ( estrogen elevation and RAAS activation; also a cause in pregnancy associated edema)
*Idiopathic cyclical edema (in female)

<ref>{{cite book |title=Introductory Medical-Surgical Nursing |first1=Barbara Kuhn |last1=Timby |first2=Nancy E. |last2=Smith |year=2006 |edition=9th |location=Philadelphia |publisher=Lippincott Williams & Wilkins |page=[https://archive.org/details/introductorymedi00timb/page/488 488] |isbn=978-0-78178-032-2 |url=https://archive.org/details/introductorymedi00timb/page/488 }}</ref> [[Muscle]] action is needed not only to keep [[blood]] flowing through the [[vein]]s but also to stimulate the [[lymphatic system]] to fulfil its "overflow" function. Long-haul [[flight]]s, lengthy [[bed-rest]], immobility caused by [[disability]] and so on, are all potential causes of water retention. Even very small exercises such as rotating [[ankle]]s and wiggling [[toe]]s can help to reduce it.<ref>{{cite book |title=Lymphedema Management: The Comprehensive Guide for Practitioners |first=Joachim E. |last=Zuther |year=2005 |edition=1st |location=New York |publisher=[[Thieme Medical Publishers]] |page=222 |isbn=978-1-58890-284-9 |url=https://archive.org/details/lymphedemamanage00joac/page/222 }}</ref>

Certain [[medications]] are prone to causing water retention. These include [[estrogen]]s, thereby including drugs for [[hormone replacement therapy (menopause)|hormone replacement therapy]] or the [[combined oral contraceptive pill]],<ref>{{cite web |url=http://www.merck.com/mmpe/lexicomp/estrogens%20(conjugated-equine).html |title=Estrogens (Conjugated/Equine) |work=The Merck Manual |access-date=9 August 2017 |archive-url=https://web.archive.org/web/20071202133613/http://www.merck.com/mmpe/lexicomp/estrogens%20(conjugated-equine).html |archive-date=2 December 2007}}</ref> as well as [[non-steroidal anti-inflammatory drugs]] and [[beta-blockers]].<ref>{{cite web |url=http://www.webmd.com/hypertension-high-blood-pressure/hypertension-treatment-beta-blockers |title=Beta-Blockers for High Blood Pressure |work=[[WebMD]] |access-date=9 August 2017}}</ref>

[[Premenstrual water retention]], causing [[bloating]] and [[breast tenderness]], is common.<ref name="Copstead-KirkhornBanasik2014">{{cite book|author1=Lee-Ellen C. Copstead-Kirkhorn|author2=Jacquelyn L. Banasik|title=Pathophysiology|url=https://books.google.com/books?id=i7jwAwAAQBAJ&pg=PA660|date=25 June 2014|publisher=Elsevier Health Sciences|isbn=978-0-323-29317-4|pages=660–}}</ref><ref name="pmid19099613">{{cite journal | vauthors = Farage MA, Neill S, MacLean AB | title = Physiological changes associated with the menstrual cycle: a review | journal = Obstet Gynecol Surv | volume = 64 | issue = 1 | pages = 58–72 | year = 2009 | pmid = 19099613 | doi = 10.1097/OGX.0b013e3181932a37 | s2cid = 22293838 }}</ref><ref name="Pooler2009">{{cite book|author=Charlotte Pooler|title=Porth Pathophysiology: Concepts of Altered Health States|url=https://books.google.com/books?id=2-MFXOEG0lcC&pg=PA1075|date=1 October 2009|publisher=Lippincott Williams & Wilkins|isbn=978-1-60547-781-7|pages=1075, 1107}}</ref>

== Mechanism ==
Six factors can contribute to the formation of edema:<ref>{{cite book |last1=Scallan |first1=Joshua |last2=Huxley |first2=Virginia H. |last3=Korthuis |first3=Ronald J. |title=Pathophysiology of Edema Formation |date=2010 |publisher=Morgan & Claypool Life Sciences |url=https://www.ncbi.nlm.nih.gov/books/NBK53445/ |access-date=11 July 2022 |language=en}}</ref>
# increased [[hydrostatic pressure]];
# reduced colloidal or [[oncotic pressure]] within blood vessels;
# increased tissue colloidal or  oncotic pressure;
# increased blood vessel wall permeability (such as [[inflammation]]);
# obstruction of fluid clearance in the [[lymphatic system]];
# changes in the water-retaining properties of the tissues themselves. Raised hydrostatic pressure often reflects retention of water and sodium by the kidneys.<ref>{{cite book| author=Kumar|author2=Abbas|author3=Fausto |title=Pathologic Basis of Disease |edition=7th |publisher=Elsevier Saunders |year=1999 |pages=122 |isbn= 0-7216-0187-1}}</ref>
Generation of interstitial fluid is regulated by the forces of the [[Starling equation]].<ref>{{cite book | last1= Boron | first1= W. F. | last2= Boulpaep | first2= E. L. | year = 2012| title = Medical Physiology: A Cellular and Molecular Approach| chapter = 2e| publisher =Saunders/Elsevier| place = Philadelphia| pages =| isbn=}}</ref> Hydrostatic pressure within blood vessels tends to cause water to filter out into the tissue. This leads to a difference in protein concentration between blood plasma and tissue. As a result, the colloidal or [[oncotic pressure]] of the higher level of protein in the plasma tends to draw water back into the blood vessels from the tissue. Starling's equation states that the rate of leakage of fluid is determined by the difference between the two forces and also by the permeability of the vessel wall to water, which determines the rate of flow for a given force imbalance. Most water leakage occurs in capillaries or post capillary [[venule]]s, which have a [[semi-permeable membrane]] wall that allows water to pass more freely than protein. (The protein is said to be reflected and the efficiency of reflection is given by a reflection constant of up to 1.) If the gaps between the cells of the vessel wall open up then permeability to water is increased first, but as the gaps increase in size permeability to protein also increases with a fall in reflection coefficient.<ref>{{cite journal |last1=Dvorak |first1=Harold F |title=Vascular permeability to plasma, plasma proteins, and cells: an update |journal=Current Opinion in Hematology |date=April 2010 |volume=17 |issue=3 |pages=225–229 |doi=10.1097/MOH.0b013e3283386638 |pmid=20375889 |pmc=2878124 }}</ref>

Changes in the variables in Starling's equation can contribute to the formation of edemas either by an increase in hydrostatic pressure within the blood vessel, a decrease in the oncotic pressure within the blood vessel or an increase in vessel wall permeability. The latter has two effects. It allows water to flow more freely and it reduces the colloidal or oncotic pressure difference by allowing protein to leave the vessel more easily.{{citation needed|date=April 2022}}

Another set of vessels known as the [[lymphatic system]] acts like an "overflow" and can return much excess fluid to the [[bloodstream]]. But even the [[lymphatic system]] can be overwhelmed, and if there is simply too much fluid, or if the [[lymphatic system]] is congested, then the fluid will remain in the tissues, causing swellings in [[human leg|leg]]s, [[ankle]]s, feet, [[abdomen]] or any other part of the body.<ref>{{cite book |title=Essentials of Rubin's Pathology |first=Emanuel |last=Rubin |year=2008 |edition=5th |location=Philadelphia |publisher=Lippincott Williams & Wilkins |page=124 |isbn=978-0-78177-324-9}}</ref>

==Molecular biology==
The excessive [[extracellular fluid]] (interstitial fluid) in edemas is to a substantial degree caused by an increased [[Vascular permeability|permeability]] of the smallest blood vessels ([[Capillary|capillaries]]). This permeability is modulated by numerous biochemical chain reactions and can therefore be unbalanced by many influences.<ref name="pmid33744890">{{cite journal| author=Cai A, Chatziantoniou C, Calmont A| title=Vascular Permeability: Regulation Pathways and Role in Kidney Diseases. | journal=Nephron | year= 2021 | volume= 145 | issue= 3 | pages= 297–310 | pmid=33744890 | doi=10.1159/000514314 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=33744890  | archive-url=https://web.archive.org/web/20240727185649/https://karger.com/nef/article/145/3/297/227114/Vascular-Permeability-Regulation-Pathways-and-Role  | url-status=dead  | archive-date=July 27, 2024  }} </ref>

Involved in these processes are, among others, the [[transmembrane protein]]s [[occludin]], [[claudin]]s, [[tight junction protein ZO-1]], [[cadherin]]s, [[catenin]]s and [[actinin]], which are directed by intracellular signal chains, in particular in connection with the [[enzyme]] [[protein kinase C]].<ref name="pmid17554565">{{cite journal| author=Doucet A, Favre G, Deschênes G| title=Molecular mechanism of edema formation in nephrotic syndrome: therapeutic implications. | journal=Pediatr Nephrol | year= 2007 | volume= 22 | issue= 12 | pages= 1983–90 | pmid=17554565 | doi=10.1007/s00467-007-0521-3 | pmc=2064946 }} </ref>

==Diagnosis==
{| class="wikitable sortable" align="right"
|+Grading of edema<ref>[http://www.unicef.org/nutrition/training/3.1/20.html Nutrition in Emergencies > Measuring œdema] {{Webarchive|url=https://web.archive.org/web/20170218035923/https://www.unicef.org/nutrition/training/3.1/20.html |date=2017-02-18 }}. Erin Boyd, reviewed by Diane Holland, Nutrition in Emergencies Unit, [[UNICEF]]. Retrieved Nov 2012</ref>
|-
!scope="col"| Grade
!scope="col"| Definition
|-
!scope="row"| Absent
| Absent
|-
!scope="row"| +
| Mild: Both feet / ankles
|-
!scope="row"| ++
| Moderate: Both feet,<br> plus lower legs,<br> hands or lower arms
|-
!scope="row"| +++
| Severe: Generalised<br> bilateral pitting edema,<br> including both feet,<br> legs, arms and face
|}

Edema may be described as '''pitting edema''' or '''non-pitting edema'''.<ref name="webmd">{{cite web |last1=Booth |first1=Stephanie |title=Pitting Edema |url=https://www.webmd.com/heart-disease/pitting-edema |website=WebMD |access-date=1 January 2023 |language=en}}</ref> Pitting edema is when, after pressure is applied to a small area, the indentation persists after the release of the pressure. [[Peripheral edema|Peripheral]] pitting edema, as shown in the illustration, is the more common type, resulting from water retention. It can be caused by systemic diseases, pregnancy in some women, either directly or as a result of [[heart failure]], or local conditions such as [[varicose veins]], [[thrombophlebitis]], insect bites, and [[dermatitis]].<ref>{{cite book |title=Causes and signs of edema |date=30 December 2016 |publisher=Institute for Quality and Efficiency in Health Care (IQWiG) |url=https://www.ncbi.nlm.nih.gov/books/NBK279409/ |access-date=26 July 2022 |language=en}}</ref>

Non-pitting edema is observed when the indentation does not persist. It is associated with such conditions as [[lymphedema]], [[lipedema]], and [[myxedema]].

Edema caused by malnutrition defines [[kwashiorkor]], an acute form of childhood protein-energy malnutrition characterized by edema, irritability, anorexia, [[Ulcerative dermatitis|ulcerating dermatoses]], and an enlarged liver with fatty infiltrates.

==Treatment==
{{multiple image|

<!-- Image 1 -->
| image1    = Case 11-leftN.PNG
| width1    = 116
| alt1      = A man with a swollen face
| caption1  = Vein obstruction causes facial edema while lying down to sleep.

<!-- Image 2 -->
| image2    = Case 11-rightN.png
| width2    = 180
| alt2      = The same man with no swelling in his face
| caption2  = After being upright all day, the swelling disappears.
}}

When possible, treatment involves resolving the underlying cause. Many cases of [[heart]] or [[kidney]] disease are treated with [[diuretics]].<ref name=":0" />

Treatment may also involve positioning the affected body parts to improve drainage. For example, swelling in feet or ankles may be reduced by having the person lie down in bed or sit with the feet propped up on cushions. [[Intermittent pneumatic compression]] can be used to pressurize tissue in a limb, forcing fluids—both blood and [[lymph]]—to flow out of the compressed area.<ref>{{cite journal |last1=Zaleska |first1=Marzanna |last2=Olszewski |first2=Waldemar L. |last3=Cakala |first3=Marta |last4=Cwikla |first4=Jaroslaw |last5=Budlewski |first5=Tadeusz |title=Intermittent Pneumatic Compression Enhances Formation of Edema Tissue Fluid Channels in Lymphedema of Lower Limbs |journal=Lymphatic Research and Biology |date=June 2015 |volume=13 |issue=2 |pages=146–153 |doi=10.1089/lrb.2014.0010 |pmid=25748341 |pmc=4492553 }}</ref>
{{-}}

== References ==
{{reflist}}

== External links ==
{{Commons category|Edema}}
{{Medical condition classification and resources
|  DiseasesDB     = 9148
|  ICD10          = {{ICD10|R|60|9|r|50}}
|  ICD9           =  {{ICD9|782.3}}
|  ICDO           =
|  OMIM           =
|  MedlinePlus    = 003103
|  eMedicineSubj =
|  eMedicineTopic =
|  MeshID         = D004487
|}}
{{Skin and subcutaneous tissue symptoms and signs}}
{{Disorders of volume state}}
{{Authority control}}

[[Category:Causes of death]]
[[Category:Medical signs]]
[[Category:Lymphatic vessel diseases]]
[[Category:Wikipedia medicine articles ready to translate]]