View source for Breast

{{Short description|Part of the female primate torso that has mammary glands}}
{{Other uses}}
{{Pp|small=yes}}
{{Pp-move}}
{{Use dmy dates|date=November 2024}}
{{Use American English|date=November 2024}}
{{Infobox anatomy
| Name        = Breast
| Latin       = {{noitalic|{{wikt-lang|la|mamma}} ({{lang|la|mammalis}} 'of the breast')<ref>
{{cite web |url=http://dictionary.reference.com/browse/mammal |title=mammal |publisher=Dictionary.reference.com |access-date=31 October 2011 |archive-url=https://web.archive.org/web/20111114204020/http://dictionary.reference.com/browse/mammal |archive-date=14 November 2011 |url-status=live }}</ref>}}
| Image       = Weibliche brust en.jpg
| Caption     = [[Morphology (biology)|Morphology]] of female human breasts, with the [[areola]], [[nipple]], and [[inframammary fold]]
| Image2      = File:Chest young male yellow.jpg
| Caption2    = Male human breasts with defined [[pectoral muscle]]s
| Precursor   =
| System      =
| Artery      = [[Internal thoracic artery]]
| Vein        = [[Internal thoracic vein]]
| Nerve       =
| Lymph       =
}}
The '''breasts''' are two prominences located on the upper [[ventral]] region of the [[torso]] among humans and other [[primate]]s. Both sexes develop breasts from the same [[embryology|embryological]] [[Tissue (biology)|tissues]]. The relative size and [[development of the breasts]] is a major [[secondary sex distinction]] between females and males. There is also considerable [[Bra size|variation in size]] between individuals. Permanent breast growth during [[puberty]] is caused by [[estrogens]] in conjunction with the [[growth hormone]]. Female humans are the only [[mammal]]s that permanently develop breasts at puberty; all other mammals develop their [[mammary tissue]] during the latter period of [[pregnancy]]. 

In females, the breast serves as the mammary gland, which produces and secretes [[Breast milk|milk]] to [[Breastfeeding|feed infants]].<ref>
{{cite web |url = http://www.merriam-webster.com/dictionary/breast |title = Breast – Definition of breast |work = Merriam-Webster |access-date = 21 October 2015 |archive-url = https://web.archive.org/web/20150906013636/http://www.merriam-webster.com/dictionary/breast |archive-date = 6 September 2015 |url-status = live }}</ref> [[Subcutaneous fat]] covers and envelops a network of [[lactiferous duct|ducts]] that converge on the [[nipple]], and these tissues give the breast its distinct size and globular shape. At the ends of the ducts are lobules, or clusters of [[Mammary alveolus|alveoli]], where milk is produced and stored in response to [[hormone|hormonal signals]].<ref name=SEER>
{{cite web |title = SEER Training: Breast Anatomy |url = http://training.seer.cancer.gov/breast/anatomy/ |publisher = National Cancer Institute |access-date = 9 May 2012 |archive-url = https://web.archive.org/web/20120502155537/http://training.seer.cancer.gov/breast/anatomy/ |archive-date = 2 May 2012 |url-status = live }}
</ref> During pregnancy, the breast responds to a complex interaction of hormones, including [[estrogen]]s, [[progesterone]], and [[prolactin]], that mediate the completion of its development, namely lobuloalveolar maturation, in preparation of [[lactation]] and breastfeeding.

Along with their major function in providing nutrition for infants, breasts can figure prominently in the perception of a [[Female body|woman's body]] and [[Sexual attraction|sexual attractiveness]]. Breasts, especially the nipples, can be an [[erogenous zone]], and part of [[sexual activity]]. Some cultures ascribe social and [[Sexualization|sexual characteristics]] to female breasts, and may regard [[Bare breasted|bare breasts]] in [[Public nudity|public]] as [[immodest]] or [[indecent]]. Breasts can represent [[fertility]], [[femininity]], or [[Cornucopia|abundance]]. Breasts have been featured in ancient and modern sculpture, art, and photography.

==Etymology and terminology==
The English word ''breast'' derives from the [[Old English]] word {{lang|ang|brēost}} {{Gloss|breast, bosom}} from [[Proto-Germanic]] {{lang|gem-x-proto|breustam}} {{Gloss|breast}}, from the [[Proto-Indo-European]] base {{lang|ine-x-proto|bhreus–}} {{Gloss|to swell, to sprout}}.<ref>{{cite web |title=Indo-European Lexicon |url=http://www.utexas.edu/cola/centers/lrc/ielex/PokornyMaster-X.html |archive-url=https://web.archive.org/web/20160420225029/http://www.utexas.edu/cola/centers/lrc/ielex/PokornyMaster-X.html |archive-date=20 April 2016 |website=The University of Texas at Austin }}</ref> The ''breast'' spelling conforms to the Scottish and North English dialectal pronunciations.<ref>
{{cite web |title=breast |url=http://www.etymonline.com/index.php?term=breast |url-status=live |archive-url=https://web.archive.org/web/20120202185418/http://www.etymonline.com/index.php?term=breast |archive-date=2 February 2012 |access-date=7 March 2011 |website=Online Etymology Dictionary }}
</ref> The ''Merriam-Webster Dictionary'' states that "[[Middle English]] {{lang|enm|brest}}, [comes] from Old English {{lang|ang|brēost}}; akin to [[Old High German]] {{lang|goh|brust}}..., [[Old Irish]] {{lang|sga|brú}} [belly], [and] Russian {{lang|ru-Latn|bryukho}}"; the first known usage of the term was before the 12th century.<ref>
{{cite web |title=Definition of breast |url=https://www.merriam-webster.com/dictionary/breast |url-status=live |archive-url=https://web.archive.org/web/20161220084629/https://www.merriam-webster.com/dictionary/breast |archive-date=20 December 2016 |access-date=10 December 2016 |website=Dictionary by Merriam-Webster }}
</ref>

''Breasts'' is often used to refer to female breasts in particular, though the stricter anatomical term refers to the same region on members of either sex. Male breasts are sometimes referred to in the singular to mean the collective upper chest area,{{efn|Such that one's hands might be folded "upon one's breast" or one's heart might be "within one's breast"}} whereas female breasts are referred to in the plural unless speaking of a specific left or right breast.

A large number of colloquial terms for female breasts are used in English, ranging from fairly polite terms to vulgar or slang.{{efn|See [[Wiktionary:Thesaurus:breasts]]}} Some vulgar slang expressions may be considered to be derogatory or sexist to women.<ref>{{cite web |last=Groot |first=Sue de |date=18 September 2016 |title=Is there a respectful slang word for breasts? |url=https://www.timeslive.co.za/sunday-times/lifestyle/2016-09-18-is-there-a-respectful-slang-word-for-breasts/ |url-status=live |archive-url=https://web.archive.org/web/20161211114217/http://www.timeslive.co.za/sundaytimes/lifestyle/opinion/article1754258.ece |archive-date=11 December 2016 |access-date=11 December 2016 |website=Sunday Times }}</ref>

==Evolutionary development==
[[File:Mountain gorilla breast feeding.KMRA.jpg|thumb|[[Mountain gorilla]] breastfeeding an infant]]
Humans are the only mammals whose breasts become permanently enlarged after [[sexual maturity]] (known in humans as [[puberty]]). The reason for this evolutionary change is unknown.<ref name="DM">{{Cite web |last=Alex |first=Bridget |date=6 March 2019 |title=Scientists Still Stumped by the Evolution of Human Breasts |url=https://www.discovermagazine.com/planet-earth/scientists-still-stumped-by-the-evolution-of-human-breasts |url-status=live |archive-url=https://web.archive.org/web/20220204163722/https://www.discovermagazine.com/planet-earth/scientists-still-stumped-by-the-evolution-of-human-breasts |archive-date=4 February 2022 |access-date=4 February 2022 |website=[[Discover (magazine)|Discover]]}}</ref> Several hypotheses have been put forward:

A link has been proposed to processes for synthesizing the [[endogenous]] [[steroid hormone]] precursor [[dehydroepiandrosterone]] which takes place in fat rich regions of the body like the buttocks and breasts. These contributed to human brain development and played a part in increasing brain size.  Breast enlargement may for this purpose have occurred as early as ''[[Homo ergaster]]'' (1.7–1.4 [[myr|MYA]]).<ref name=":2" /> Other breast formation hypotheses may have then taken over as principal drivers.<ref>{{Cite journal|last1=LeBlanc|first1=Steven A.|last2=Barnes|first2=Ethne|date=July 1974|title=On the Adaptive Significance of the Female Breast|journal=The American Naturalist|volume=108|issue=962|pages=577–578|doi=10.1086/282935|bibcode=1974ANat..108..577L |s2cid=85243414|issn=0003-0147}}</ref><ref name=":1">{{Cite journal|last1=Howard|first1=Beatrice A.|last2=Veltmaat|first2=Jacqueline M.|date=18 May 2013|title=Embryonic Mammary Gland Development; a Domain of Fundamental Research with High Relevance for Breast Cancer Research|journal=Journal of Mammary Gland Biology and Neoplasia|volume=18|issue=2|pages=89–91|doi=10.1007/s10911-013-9296-2|pmid=23686554|s2cid=1657065|issn=1083-3021|doi-access=free}}</ref><ref name=":2">{{Cite journal|last1=Pawłowski|first1=Bogusław|last2=Żelaźniewicz|first2=Agnieszka|date=2021|title=The evolution of perennially enlarged breasts in women: a critical review and a novel hypothesis|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/brv.12778|journal=Biological Reviews|language=en|volume=96|issue=6|pages=2794–2809|doi=10.1111/brv.12778|pmid=34254729|s2cid=235807642|issn=1469-185X|access-date=30 November 2021|archive-date=30 November 2021|archive-url=https://web.archive.org/web/20211130190318/https://onlinelibrary.wiley.com/doi/abs/10.1111/brv.12778|url-status=live|url-access=subscription}}</ref>

It has been suggested by zoologists Avishag and [[Amotz Zahavi]] that the size of the human breasts can be explained by the [[Handicap principle|handicap theory]] of [[sexual dimorphism]]. This would see the explanation for larger breasts as them being an [[Signalling theory|honest display]] of the women's health and ability to grow and carry them in her life. Prospective mates can then evaluate the genes of a potential mate for their ability to sustain her health even with the additional energy demanding burden she is carrying.<ref>Geoffrey Miller: ''The Sexual Evolution. Choice of partner and the emergence of the mind.'' Spectrum Academic Publishing House, 2009, {{ISBN|978-3-8274-2508-9}}</ref><ref name=":0">{{cite journal |last1=Pawłowski |first1=Bogusław |last2=Żelaźniewicz |first2=Agnieszka |date=13 July 2021 |title=The evolution of perennially enlarged breasts in women: a critical review and a novel hypothesis |journal=Biological Reviews |volume=96 |issue=6 |pages=2794–2809 |doi=10.1111/brv.12778 |pmid=34254729 |s2cid=235807642| issn=0006-3231 }}</ref>

The zoologist [[Desmond Morris]] describes a sociobiological approach in his science book ''[[The Naked Ape]]''. He suggests, by making comparisons with the other primates, that breasts evolved to replace swelling buttocks as a sex signal of ovulation. He notes how humans have, relatively speaking, large penises as well as large breasts. Furthermore, early humans adopted bipedalism and face-to-face coitus. He therefore suggested enlarged sexual signals helped maintain the bond between a mated male and female even though they performed different duties and therefore were separated for lengths of time.<ref>{{Cite web |last1=Dunbar |first1=Robin |last2=Saini |first2=Angela |last3=Garrod |first3=Ben |last4=Rutherford |first4=Adam |date=24 September 2017 |title=The Naked Ape at 50: 'Its central claim has surely stood the test of time ' |url=http://www.theguardian.com/science/2017/sep/24/the-naked-ape-at-50-desmond-morris-four-experts-assess-impact |url-status=live |archive-url=https://web.archive.org/web/20211116160057/https://www.theguardian.com/science/2017/sep/24/the-naked-ape-at-50-desmond-morris-four-experts-assess-impact |archive-date=16 November 2021 |access-date=24 November 2021 |website=The Guardian |language=en}}</ref><ref name=":0" /><ref>{{Cite web |last=Binns |first=Corey |date=5 August 2010 |title=Why Do Women Have Breasts? |url=https://www.livescience.com/32745-why-do-women-have-breasts.html |url-status=live |archive-url=https://web.archive.org/web/20211124171609/https://www.livescience.com/32745-why-do-women-have-breasts.html |archive-date=24 November 2021 |access-date=24 November 2021 |website=Live Science |language=en}}</ref>

A 2001 study proposed that the rounded shape of a woman's breast evolved to prevent the sucking infant offspring from suffocating while feeding at the teat; that is, because of the human infant's small jaw, which did not project from the face to reach the nipple, they might block the [[Nose|nostrils]] against the mother's breast if it were of a flatter form (compare with the [[common chimpanzee]]). Theoretically, as the human jaw receded into the face, the woman's body compensated with round breasts.<ref name="Bentley">{{cite journal |last = Bentley |first = Gillian R. |year = 2001 |title = The evolution of the human breast |journal = American Journal of Physical Anthropology |volume = 32 |issue = 38 |doi = 10.1002/ajpa.1033 |pages = 30–50 }}</ref>

[[Ashley Montagu]] (1965) proposed that breasts came about as an adaptation for infant feeding for a different reason, as early human ancestors adopted bipedalism and the loss of body hair.  Human upright stance meant infants must be carried at the hip or shoulder instead of on the back as in the apes. This gives the infant less opportunity to find the nipple or the purchase to cling on to the mother's body hair.  The mobility of the nipple on a large breast in most human females gives the infant more ability to find it, grasp it and feed.<ref name=":1" />

Other suggestions include simply that permanent breasts attracted mates, that "pendulous" breasts gave infants something to cling to, or that permanent breasts shared the function of a [[Camel#Hump|camel's hump]], to store fat as an energy reserve.<ref name="DM"/>

== Structure ==
[[File:Breast anatomy normal scheme.png|thumb|upright=1.35|The breast: cross-section scheme of the [[mammary gland]]. {{ordered list |[[Chest wall]] |[[Pectoralis muscle]]s |[[Lobules]] |[[Nipple]] |[[Areola]] |[[Lactiferous duct|Milk duct]] |[[Adipose tissue|Fatty tissue]] |Skin}}]]

In women, the breasts overlie the [[pectoralis major muscle]]s and extend on average from the level of the second rib to the level of the sixth rib in the front of the [[human rib cage|rib cage]]; thus, the breasts cover much of the chest area and the chest walls. At the front of the chest, the '''breast tissue''' can extend from the [[clavicle]] (collarbone) to the middle of the [[sternum]] (breastbone). At the sides of the chest, the breast tissue can extend into the [[axilla]] (armpit), and can reach as far to the back as the [[latissimus dorsi muscle]], extending from the lower back to the [[humerus]] bone (the bone of the upper arm). As a [[mammary gland]], the breast is composed of differing layers of [[Histology|tissue]], predominantly two types: [[adipose tissue]]; and [[Lactiferous duct|glandular tissue]], which affects the lactation functions of the breasts.<ref name=GRAYS2005>{{cite book |last = Drake |first = Richard L. |title = Gray's anatomy for students |year = 2005 |publisher = Elsevier/Churchill Livingstone |location = Philadelphia |isbn = 978-0-8089-2306-0 |author2 = Vogl, Wayne |author3 = Tibbitts, Adam W.M. Mitchell |others = illustrations by Richard Richardson, Paul }}</ref>{{rp|115}} The natural [[resonant frequency]] of the human breast is about 2 [[hertz]].<ref>{{cite book |last1=Cameron |first1=John R. |last2=Skofronick |first2=James G. |last3=Grant |first3=Roderick M. |title=Physics of the Body |date=1999 |publisher=Medical Physics Publishing |location=Madison, Wis |isbn=978-0-944838-91-4 |pages=69–70 |edition=2nd |url=https://medicalphysics.org/SimpleCMS.php?content=bookpage.php&isbn=9781930524941}}</ref>

[[Morphology (biology)|Morphologically]], the breast is tear-shaped.<ref name="love_c1">{{cite book|last1=Love|first1=Susan M.|title=Dr. Susan Love's Breast Book|date=2015|publisher=Da Capo Press|location=U.S.|isbn=978-07382-1821-2|edition=6|chapter=1}}</ref> The superficial tissue layer ([[superficial fascia]]) is separated from the skin by 0.5–2.5&nbsp;cm of subcutaneous fat (adipose tissue). The [[Cooper's ligaments|suspensory Cooper's ligaments]] are fibrous-tissue prolongations that radiate from the superficial fascia to the skin envelope. The female adult breast contains 14–18 irregular lactiferous lobes that converge at the nipple. The 2.0–4.5&nbsp;mm milk ducts are immediately surrounded with dense connective tissue that support the glands. Milk exits the breast through the nipple, which is surrounded by a pigmented area of skin called the areola. The size of the areola can vary widely among women. The areola contains modified [[sebaceous gland|sweat glands]] known as [[Areolar gland|Montgomery's glands]]. These glands secrete oily fluid that lubricate and protect the nipple during breastfeeding.<ref name=stoppler>{{cite web |last1 = Stöppler |first1 = Melissa Conrad |title = Breast Anatomy |url = http://www.medicinenet.com/breast_anatomy/article.htm |access-date = 28 June 2015 |archive-url = https://web.archive.org/web/20150627065040/http://www.medicinenet.com/breast_anatomy/article.htm |archive-date = 27 June 2015 |url-status = live }}</ref> Volatile compounds in these secretions may also serve as an olfactory stimulus for the newborn's appetite.<ref>{{cite journal |doi = 10.1371/journal.pone.0007579 |title = The Secretion of Areolar (Montgomery's) Glands from Lactating Women Elicits Selective, Unconditional Responses in Neonates |year = 2009 |editor1-last = Hausberger |editor1-first = Martine |last1 = Doucet |first1 = Sébastien |last2 = Soussignan |first2 = Robert |last3 = Sagot |first3 = Paul |last4 = Schaal |first4 = Benoist |journal = PLOS ONE |volume = 4 |issue = 10 |article-number = e7579 |pmid = 19851461 |pmc = 2761488 |bibcode = 2009PLoSO...4.7579D |doi-access = free }}</ref>
[[File:Areolar enlargement.png|thumb|Breasts during early pregnancy, showing enlarged [[areolar gland]]s]]
The dimensions and weight of the breast vary widely among women. A small-to-medium-sized breast weighs 500&nbsp;grams (1.1 pounds) or less, and a large breast can weigh approximately 750 to 1,000 grams (1.7 to 2.2 pounds) or more. In terms of composition, the breasts are about 80 to 90% [[stroma (tissue)|stroma]]l tissue ([[adipose tissue|fat]] and [[connective tissue]]), while [[epithelial tissue|epithelial]] or [[gland]]ular tissue only accounts for about 10 to 20% of the volume of the breasts.<ref name="pmid16728564">{{cite journal |vauthors=Lorincz AM, Sukumar S |title=Molecular links between obesity and breast cancer |journal=Endocrine-Related Cancer |volume=13 |issue=2 |pages=279–92 |year=2006 |pmid=16728564 |doi=10.1677/erc.1.00729 |quote=Adipocytes make up the bulk of the human breast, with epithelial cells accounting for only approximately 10% of human breast volume.|doi-access=free}}</ref><ref name="pmid11149569">{{cite journal |vauthors=Howard BA, Gusterson BA |title=Human breast development |journal=Journal of Mammary Gland Biology and Neoplasia |volume=5 |issue=2 |pages=119–37 |year=2000 |pmid=11149569 |doi= 10.1023/A:1026487120779|s2cid=10819224 |quote=In the stroma, there is an increase in the amount of fibrous and fatty tissue, with the adult nonlactating breast consisting of 80% or more of stroma.}}</ref><ref name="RosenfieldCookeRadovick2021">{{cite book | title = Sperling Pediatric Endocrinology | last1 = Rosenfield | first1 = Robert L. | last2 = Cooke | first2 = David W. | last3 = Radovick | first3 = Sally | chapter = Puberty in the Female and Its Disorders | date = 2021 | pages = 528–626 | publisher = Elsevier | doi = 10.1016/B978-0-323-62520-3.00016-6 | isbn = 978-0-323-62520-3 | s2cid = 234131890 | chapter-url = https://books.google.com/books?id=8J7yDwAAQBAJ&pg=PA554 | quote = Estrogen stimulates the nipples to grow, mammary terminal duct branching to progress to the stage at which ductules are formed, and fatty stromal growth to increase until it constitutes about 85% of the mass of the breast. [...] Lobulation appears around menarche, when multiple blind saccular buds form by branching of the terminal ducts. These effects are due to the presence of progesterone. [...] Full alveolar development normally only occurs during pregnancy under the influence of additional progesterone and prolactin.}}</ref><ref name="pmid22206682">{{cite journal |vauthors=Hagisawa S, Shimura N, Arisaka O |title=Effect of excess estrogen on breast and external genitalia development in growth hormone deficiency |journal=Journal of Pediatric and Adolescent Gynecology |volume=25 |issue=3 |pages=e61–3 |year=2012 |pmid=22206682 |doi=10.1016/j.jpag.2011.11.005 |quote=Estrogen stimulates growth of the nipples, progression of mammary duct branching to the stage at which ductiles are formed, and fatty stromal growth until it constitutes about 85% of the mass of the breast.}}</ref><ref name="pmid2942075">{{cite journal | vauthors = Drife JO | title = Breast development in puberty | journal = Ann N Y Acad Sci | volume = 464 | issue = 1| pages = 58–65 | date = 1986 | pmid = 2942075 | doi = 10.1111/j.1749-6632.1986.tb15993.x | bibcode = 1986NYASA.464...58D | s2cid = 12735704 | url = | quote = Along with the glandular growth, there is an increase in the amount of fibrous and fatty tissue, and in fact these latter two constituents of the breast account for a far greater proportion of the morphologic growth than the proportion contributed by glandular tissue. In the nonlactating adult breast, glandular tissue accounts for no more than 20% of the breast volume, and often much less than this, and the morphologic changes at puberty are therefore mainly due to stromal expansion.}}</ref> The tissue composition ratios of the breast also vary among women. Some women's breasts have a higher proportion of glandular tissue than of adipose or [[connective tissue|connective]] tissues. The fat-to-connective-tissue ratio determines the density or firmness of the breast. During a woman's life, her breasts change size, shape, and weight due to hormonal changes during [[thelarche|puberty]], the [[menstruation|menstrual cycle]], [[Maternal physiological changes in pregnancy|pregnancy]], breastfeeding, and [[menopause]].<ref>Pamplona DC, de Abreu Alvim C. Breast Reconstruction with Expanders and Implants: a Numerical Analysis. Artificial Organs 8 (2004), pp. 353–356.</ref><ref>{{cite journal |last1 = Grassley |first1 = JS |year = 2002 |title = Breast Reduction Surgery: What every Woman Needs to Know |journal = Lifelines |volume = 6 |issue = 3 |pages = 244–249 |doi = 10.1111/j.1552-6356.2002.tb00088.x |pmid = 12078570 }}</ref>

===Glandular structure===
{{Main articles|Mammary gland}}
[[File:Normal breast histology.png|thumb|Normal [[histology]] of the breast.]]

The breast is an [[apocrine]] gland that produces the [[Breast milk|milk]] used to feed an infant. The [[nipple]] of the breast is surrounded by the [[areola]] (nipple-areola complex). The areola has many sebaceous glands, and the skin color varies from pink to dark brown. The basic units of the breast are the terminal duct lobular units (TDLUs), which produce the fatty breast milk. They give the breast its offspring-feeding functions as a mammary gland. They are distributed throughout the body of the breast. Approximately two-thirds of the lactiferous tissue is within 30&nbsp;mm of the base of the nipple. The terminal lactiferous ducts drain the milk from TDLUs into 4–18 lactiferous ducts, which drain to the nipple. The milk-glands-to-fat ratio is 2:1 in a lactating woman, and 1:1 in a non-lactating woman. In addition to the milk glands, the breast is also composed of connective tissues ([[collagen]], [[elastin]]), white fat, and the suspensory Cooper's ligaments. Sensation in the breast is provided by the [[peripheral nervous system]] innervation by means of the front (anterior) and side (lateral) cutaneous branches of the fourth-, fifth-, and sixth [[intercostal nerves]]. The T-4 nerve ([[Thoracic spinal nerve 4]]), which innervates the [[dermatomic area]], supplies sensation to the nipple-areola complex.<ref name=grabowski>{{cite book |first1 = Gerard J. |last1 = Tortora |first2 = Sandra Reynolds |last2 = Grabowski |title = Introduction to the Human Body: the Essentials of Anatomy and Physiology |date = 2001 |publisher = J. Wiley |location = New York; Toronto |isbn = 978-0-471-36777-2 |edition = Fifth. }}</ref>

===Lymphatic drainage===
Approximately 75% of the [[lymph]] from the breast travels to the axillary [[lymph node]]s on the same side of the body, while 25% of the lymph travels to the parasternal nodes (beside the sternum bone).<ref name=GRAYS2005 />{{rp|116}} A small amount of remaining lymph travels to the other breast and to the abdominal lymph nodes. The subareolar region has a lymphatic plexus known as the "subareolar plexus of Sappey".<ref name="Pacifici">{{cite web |last1=Pacifici |first1=Stefano |title=Sappey plexus {{!}} Radiology Reference Article {{!}} Radiopaedia.org |url=https://radiopaedia.org/articles/sappey-plexus-1?lang=gb |website=Radiopaedia |date=11 October 2011 |access-date=25 August 2020 |archive-date=2 May 2021 |archive-url=https://web.archive.org/web/20210502224454/https://radiopaedia.org/articles/sappey-plexus-1?lang=gb |url-status=live }}</ref> The [[axillary lymph node]]s include the pectoral (chest), subscapular (under the scapula), and humeral (humerus-bone area) lymph-node groups, which drain to the central [[axillary lymph nodes]] and to the apical axillary lymph nodes. The lymphatic drainage of the breasts is especially relevant to [[oncology]] because breast cancer is common to the mammary gland, and cancer cells can [[Metastasis|metastasize]] (break away) from a [[tumor]] and be dispersed to other parts of the body by means of the lymphatic system.

===Morphology===
{{Multiple image
| image1            = Breasts of a woman.jpg
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| image4            = Breasts close-up (4).jpg
}}

The morphologic variations in the size, shape, volume, tissue density, pectoral locale, and spacing of the breasts determine their natural shape, appearance, and position on a woman's chest. [[Breast size]] and other characteristics do not predict the fat-to-milk-gland ratio or the potential for the woman to nurse an infant. The size and the shape of the breasts are influenced by normal-life hormonal changes (thelarche, menstruation, pregnancy, menopause) and medical conditions (e.g. [[virginal breast hypertrophy]]).<ref name=wood>{{cite journal |vauthors = Wood K, Cameron M, Fitzgerald K |title = Breast Size, Bra Fit and Thoracic Pain in Young Women: A Correlational Study |journal = Chiropractic & Osteopathy |volume = 16 |article-number = 1 |year = 2008 |pmid = 18339205 |pmc = 2275741 |doi = 10.1186/1746-1340-16-1 |doi-access = free }}</ref> The shape of the breasts is naturally determined by the support of the suspensory Cooper's ligaments, the underlying muscle and bone structures of the chest, and by the skin envelope. The suspensory ligaments sustain the breast from the clavicle (collarbone) and the clavico-pectoral fascia (collarbone and chest) by traversing and encompassing the fat and milk-gland tissues. The breast is positioned, affixed to, and supported upon the chest wall, while its shape is established and maintained by the skin envelope.<ref>{{Cite web |title=Breast Anatomy – Breast360.org {{!}} The American Society of Breast Surgeons Foundation |url=https://breast360.org/topic/2017/01/01/breast-anatomy/ |access-date=2024-12-21 |website=breast360.org}}</ref><ref>{{Cite web |title=Breast Anatomy {{!}} SEER Training |url=https://training.seer.cancer.gov/breast/anatomy/ |access-date=2024-12-21 |website=training.seer.cancer.gov}}</ref> In most women, one breast is slightly larger than the other.<ref name=love_c1/> More obvious and persistent asymmetry in breast size occurs in up to 25% of women.<ref name=mgh2010>{{cite web |url = http://www.mgh.harvard.edu/children/adolescenthealth/articles/aa_breast_development.aspx |title = Breast Development |publisher = Massachusetts Hospital for Children |access-date = 2 June 2010 |archive-url = https://web.archive.org/web/20101225165742/http://www.mgh.harvard.edu/children/adolescenthealth/articles/aa_breast_development.aspx |archive-date = 25 December 2010 }}</ref>

The base of each breast is attached to the chest by the deep fascia over the pectoralis major muscles. The base of the breast is semi-circular, however the shape and position of the breast above the surface is variable.<ref>{{Citation |last=Gould |first=Stanley F. |title=Anatomy of the Breast |date=1983 |work=Lactation: Physiology, Nutrition, and Breast-Feeding |pages=23–47 |editor-last=Neville |editor-first=Margaret C. |url=https://link.springer.com/chapter/10.1007/978-1-4613-3688-4_2 |access-date=2024-12-25 |place=Boston, MA |publisher=Springer US |language=en |doi=10.1007/978-1-4613-3688-4_2 |isbn=978-1-4613-3688-4 |editor2-last=Neifert |editor2-first=Marianne R.|url-access=subscription }}</ref> The space between the breast and the pectoralis major muscle, called [[retromammary space]], gives mobility to the breast. The chest ([[thoracic cavity]]) progressively slopes outwards from the thoracic inlet (atop the [[Human breastbone|breastbone]]) and above to the lowest ribs that support the breasts. The inframammary fold (IMF), where the lower portion of the breast meets the chest, is an anatomic feature created by the adherence of the breast skin and the underlying connective tissues of the chest; the IMF is the lower-most extent of the anatomic breast. Normal breast tissue has a texture that feels nodular or granular, with considerable variation from woman to woman.<ref name="love_c1" />

Breasts have been categorized into four general morphological groups:  "flat, spheric, protruded, and drooped", or "small/flat, large/inward, upward, and droopy".<ref>{{Cite journal |last1=Suh |first1=Minyoung |last2=Park |first2=Jung Hyun |date=2022-01-01 |title=Breast Geometry Characterization of Young American Females Using 3D Image Analysis |journal=Applied Sciences |language=en |volume=12 |issue=17 |page=8578 |doi=10.3390/app12178578 |doi-access=free |issn=2076-3417}}</ref><ref>{{Cite journal |title=Brassiere Pattern Development Based on 3D Measurements of Upper Body Types for Women in Their 30's |url=https://koreascience.kr/article/JAKO200827464608269.page |journal=The Research Journal of the Costume Culture|date=2008 |volume=16 |issue=3 |last1=Mi-Sook |first1=Cho }}</ref><ref>{{Cite journal |last1=Coltman |first1=Celeste E. |last2=Steele |first2=Julie R. |last3=McGhee |first3=Deirdre E. |date=2018-09-02 |title=Effects of age and body mass index on breast characteristics: a cluster analysis |url=https://www.tandfonline.com/doi/abs/10.1080/00140139.2018.1481229 |journal=Celeste E. Coltman |volume=61 |issue=9 |pages=1232–1245 |doi=10.1080/00140139.2018.1481229 |pmid=29792567 |issn=0014-0139|url-access=subscription }}</ref>

==== Support ====
{{Multiple image
| image1            = Pink underwire bra breasts close-up.jpg
| image2            = Young Woman Wearing Orange Sports Bra.jpg
| footer            = Left: Underwire bra. Right: Sports bra
| direction         = horizontal
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}}

While it is a common belief that breastfeeding causes [[Ptosis (breasts)|breasts to sag]],<ref name="lauersen">{{cite book |last = Lauersen |first = Niels H. |title = The Complete Book of Breast Care |year = 1998 |publisher = Fawcett Columbine/Ballantine |location = New York |isbn = 978-0-449-91241-6 |edition = 1st Trade Paperback |author2 = Stukane, Eileen |quote = ...there is no medical reason to wear a bra, so the decision is yours, based on your own personal comfort and aesthetics. Whether you have always worn a bra or always gone braless, age and breastfeeding will naturally cause your breasts to sag. |url = https://archive.org/details/completebookofbr00laue_0 }}</ref> researchers have found that a woman's breasts sag due to four key factors: cigarette smoking, [[gravidity|number of pregnancies]], [[gravity]], and weight loss or gain.<ref name="thompson">{{cite journal |doi = 10.1016/j.asj.2008.07.004 |title = The Effect of Breastfeeding on Breast Aesthetics |year = 2008 |last1 = Rinker |first1 = B |last2 = Veneracion |first2 = M |last3 = Walsh |first3 = C |journal = Aesthetic Surgery Journal |volume = 28 |issue = 5 |pages = 534–7 |pmid = 19083576 |doi-access = free}}
*{{cite news |author=Andrea Thompson |date=2 November 2007 |title=Breastfeeding Does Not Make Breasts Sag, Study Suggests |work=LiveScience |url = http://www.livescience.com/1998-breastfeeding-breasts-sag-study-suggests.html |access-date = 9 May 2015 |archive-url = https://web.archive.org/web/20120703153917/http://www.livescience.com/1998-breastfeeding-breasts-sag-study-suggests.html |archive-date = 3 July 2012 |url-status = live}}</ref> Women sometimes wear bras because they mistakenly believe they prevent breasts from sagging as they get older.<ref name="burn" /> Physicians, lingerie retailers, teenagers, and adult women used to believe that bras were medically required to support breasts. In a 1952 article in ''Parents' Magazine'', Frank H. Crowell erroneously reported that it was important for teen girls to begin wearing bras early. According to Crowell, this would prevent sagging breasts, stretched blood vessels, and poor circulation later on.<ref name="brumberg">{{cite book |url=http://course1.winona.msus.edu/pjohnson/e111/e111f99/brumberg.htm|archive-url=https://web.archive.org/web/20020328155254/http://course1.winona.msus.edu/pjohnson/e111/e111f99/brumberg.htm |isbn=0-679-73529-1 |page=336|title=The Body Project: An Intimate History of American Girls|archive-date=28 March 2002|first=Joan Jacobs |last=Brumberg|year=1998 |publisher=Knopf Doubleday Publishing }}</ref> This belief was based on the false idea that breasts cannot anatomically support themselves.<ref name="burn">{{cite web |title=Don't burn your bra just yet |url=https://www.independent.co.uk/life-style/health-and-families/health-news/dont-burn-your-bra-just-yet-622008.html |website=The Independent |date=22 September 2011 |access-date=8 October 2018 |archive-url=https://web.archive.org/web/20180717232012/https://www.independent.co.uk/life-style/health-and-families/health-news/dont-burn-your-bra-just-yet-622008.html |archive-date=17 July 2018 |url-status=live}}</ref><ref name="007b Breast">{{cite web |url=http://www.007b.com/why_wear_bras.php |title=Female Intelligence Agency: Why Do Women Wear Bras? |publisher=007b Breast |access-date=10 May 2011 |archive-url=https://web.archive.org/web/20110831044824/http://www.007b.com/why_wear_bras.php |archive-date=31 August 2011 |url-status=live}}</ref>

[[Sports bra]]s are sometimes used for cardiovascular exercise, sports bras are designed to secure the breasts closely to the body to prevent movement during high-motion activity such as running. Studies have indicated sports bras which are overly tight may restrict respiratory function.<ref>{{Cite journal |last1=Ocran |first1=Francisca Margarita |last2=Ji |first2=Xiaofen |last3=Zhai |first3=Lina |date=January 2022 |title=A study to evaluate pressure distribution of different sports bras |journal=Journal of Engineered Fibers and Fabrics |language=en |volume=17 |article-number=15589250221118643 |doi=10.1177/15589250221118643 |issn=1558-9250|doi-access=free }}</ref><ref>{{Cite journal |last1=Kipp |first1=Shalaya |last2=Leahy |first2=Michael G. |last3=Sheel |first3=A. William |date=2024-06-01 |title=Sports Bra Restriction on Respiratory Mechanics during Exercise |journal=Medicine and Science in Sports and Exercise |volume=56 |issue=6 |pages=1168–1176 |doi=10.1249/MSS.0000000000003403 |issn=1530-0315 |pmid=38350462}}</ref>

==Development==
{{Main|Breast development}}

The breasts are principally composed of adipose, [[glandular tissue|glandular]], and [[w:connective tissue|connective]] tissues.<ref name="yen">{{citation |title = Yen & Jaffe's Reproductive Endocrinology |author = Robert L. Barbieri |doi = 10.1016/B978-1-4160-4907-4.00010-3 |edition = 6th |publisher = Elsevier |date = 2009 |journal = Yen |pages = 235–248 |isbn = 978-1-4160-4907-4 |doi-access = free }}
</ref> Because these tissues have hormone receptors,<ref name="yen" /><ref name="gland activation">{{citation |title = Hormone Action in the Mammary Gland |author1 = Brisken |author2 = Malley |doi = 10.1101/cshperspect.a003178 |date = 2 December 2010 |pmid = 20739412 |pmc = 2982168 |volume = 2 |issue = 12 |journal = Cold Spring Harb Perspect Biol |article-number = a003178 }}</ref> their sizes and volumes fluctuate according to the hormonal changes particular to thelarche (sprouting of breasts), menstruation (egg production), pregnancy (reproduction), lactation (feeding of offspring), and menopause (end of menstruation).

===Puberty===
[[File:Female breasts five Tanner stages.jpg|thumb|Breast development in puberty is measured with the five-stage Tanner scale]]

The morphological structure of the human breast is identical in males and females until [[puberty]]. For pubescent girls in thelarche (the breast-development stage), the female [[sex hormone]]s (principally estrogens) in conjunction with [[growth hormone]] promote the sprouting, growth, and development of the breasts. During this time, the mammary glands grow in size and volume and begin resting on the chest. These development stages of [[secondary sex characteristic]]s (breasts, pubic hair, etc.) are illustrated in the five-stage [[Tanner scale]].<ref name="A.R.Greenbaum">{{cite journal |vauthors = Greenbaum AR, Heslop T, Morris J, Dunn KW |title = An Investigation of the Suitability of Bra fit in Women Referred for Reduction Mammaplasty |journal = British Journal of Plastic Surgery |volume = 56 |issue = 3 |pages = 230–6 |date = April 2003 |pmid = 12859918 |doi = 10.1016/S0007-1226(03)00122-X }}</ref>

During [[thelarche]], the developing breasts are sometimes of unequal size, and usually the left breast is slightly larger. This condition of asymmetry is transitory and statistically normal in female physical and sexual development.<ref name="asymmetry">{{cite journal |author = Loughry CW |title = Breast Volume Measurement of 598 Women using Biostereometric Analysis |journal = Annals of Plastic Surgery |year = 1989 |volume = 22 |issue = 5 |pages = 380–385 |doi = 10.1097/00000637-198905000-00002 |pmid = 2729845 |display-authors = 1 |last2 = Sheffer |first2 = Daniel B. |last3 = Price |first3 = Thomas E. |last4 = Einsporn |first4 = Richard L. |last5 = Bartfai |first5 = Ronald G. |last6 = Morek |first6 = Wayne M. |last7 = Meli |first7 = Nancy M. |s2cid = 8713713 }}</ref> Medical conditions can cause overdevelopment (e.g., virginal breast hypertrophy, [[macromastia]]) or underdevelopment (e.g., [[tuberous breast deformity]], [[micromastia]]) in girls and women.

Approximately two years after the onset of puberty (a girl's first [[menstrual cycle]]), estrogen and growth hormone stimulate the development and growth of the glandular fat and suspensory tissues that compose the breast. This continues for approximately four years until the final shape of the breast (size, volume, density) is established at about the age of 21. [[Mammoplasia]] (breast enlargement) in girls begins at puberty, unlike all other primates, in which breasts enlarge only during lactation.<ref name="stoppler" />

=== Hormone replacement therapy ===
[[File:Transsexual HRT induced developed breasts.jpg|thumb|upright|A transgender woman with HRT-induced developed breasts]]
[[Hormone replacement therapy]], including [[gender-affirming hormone therapy]], stimulates the growth of glandular and adipose tissue through estrogen supplementation.<ref>{{Cite journal |last1=De |first1=Blok Christel |last2=Klaver |first2=Maartje |last3=Nota |first3=Nienke |last4=Dekker |first4=Marieke |last5=Den |first5=Heijer Martin |date=2016-05-13 |title=Breast development in male-to-female transgender patients after one year cross-sex hormonal treatment |url=https://www.endocrine-abstracts.org/ea/0041/ea0041gp146 |journal=Endocrine Abstracts |language=en |volume=41 |doi=10.1530/endoabs.41.GP146 |issn=1470-3947|url-access=subscription }}</ref>

In menopausal women, HRT helps restore breast volume and skin elasticity diminished by declining estrogen levels, typically using oral or transdermal estradiol.<ref>{{Cite journal |title=Postmenopausal Hormone Therapy: An Endocrine Society Scientific Statement |date=2010 |pmc=6287288 |last1=Santen |first1=R. J. |last2=Allred |first2=D. C. |last3=Ardoin |first3=S. P. |last4=Archer |first4=D. F. |last5=Boyd |first5=N. |last6=Braunstein |first6=G. D. |last7=Burger |first7=H. G. |last8=Colditz |first8=G. A. |last9=Davis |first9=S. R. |last10=Gambacciani |first10=M. |last11=Gower |first11=B. A. |last12=Henderson |first12=V. W. |last13=Jarjour |first13=W. N. |last14=Karas |first14=R. H. |last15=Kleerekoper |first15=M. |last16=Lobo |first16=R. A. |last17=Manson |first17=J. E. |last18=Marsden |first18=J. |last19=Martin |first19=K. A. |last20=Martin |first20=L. |last21=Pinkerton |first21=J. V. |last22=Rubinow |first22=D. R. |last23=Teede |first23=H. |last24=Thiboutot |first24=D. M. |last25=Utian |first25=W. H. |author26=Endocrine Society |journal=The Journal of Clinical Endocrinology and Metabolism |volume=95 |issue=7 Suppl 1 |pages=s1–s66 |doi=10.1210/jc.2009-2509 |pmid=20566620 }}</ref>

In gender-affirming hormone therapy, breast development is induced through feminizing HRT, often combining estrogen with anti-androgens to suppress testosterone. Maximum growth is usually achieved after 2–3 years.<ref>{{Cite web |title=Information on Estrogen Hormone Therapy {{!}} Gender Affirming Health Program |url=https://transcare.ucsf.edu/article/information-estrogen-hormone-therapy |access-date=2024-12-02 |website=transcare.ucsf.edu}}</ref><ref>{{Cite web |title=Practical Guidelines for Transgender Hormone Treatment {{!}} Endocrinology, Diabetes, Nutrition & Weight Management |url=https://www.bumc.bu.edu/endo/clinics/transgender-medicine/guidelines/ |access-date=2024-12-02 |website=www.bumc.bu.edu}}</ref><ref>{{Cite web |title=Transgender and Gender Diverse Hormone Therapy |url=https://www.hopkinsmedicine.org/-/media/center-for-transgender-health/documents/tgd-gaht-quick-guide.ashx |website=hopkinsmedicine.org}}</ref>

Factors such as age, genetics, and hormone dosage influence outcomes.

===Changes during the menstrual cycle===
During the menstrual cycle, the breasts are enlarged by [[premenstrual water retention]] and temporary growth as influenced by changing hormone levels.<ref name="mlpswelling">{{citation |title = Breast – premenstrual tenderness and swelling |url = https://www.medlineplus.gov/ency/article/003153.htm |publisher = A.D.A.M. |date = May 2012 |access-date = 21 March 2018 |archive-url = https://web.archive.org/web/20160705060104/https://www.nlm.nih.gov/medlineplus/ency/article/003153.htm |archive-date = 5 July 2016 |url-status = live }}
</ref> 
===Pregnancy and breastfeeding===
{{Main articles|Maternal physiological changes in pregnancy|Breastfeeding}}
[[File:Breasts_with_visible_veins_on_surface.png|thumb|Postpartum breasts showing veins visible on surface]]
The breasts reach full maturity only when a woman's first pregnancy occurs.{{sfn | Lawrence | 2016 | p=34}}  Changes to the breasts are among the first signs of pregnancy. The breasts become larger, the nipple-areola complex becomes larger and darker, the [[Montgomery's glands]] enlarge, and veins sometimes become more visible. Breast tenderness during pregnancy is common, especially during the first trimester. By mid-pregnancy, the breast is physiologically capable of lactation and some women can express [[colostrum]], a form of breast milk.{{sfn | Lawrence | 2016 | p=58}}

Pregnancy causes elevated levels of the hormone [[prolactin]], which has a key role in the production of milk. However, milk production is blocked by the hormones [[progesterone]] and [[estrogen]] until after delivery, when progesterone and estrogen levels plummet.<ref name="NCBI Bookshelf 2008"/>

===Menopause===
[[File:Stretch marks on female breast.jpg|thumb|left|Breast with visible [[stretch marks]]]]{{Main article|Menopause}}
At menopause, breast atrophy occurs.<ref>{{Cite journal |title=Menopausal Transition, Body Mass Index, and Prevalence of Mammographic Dense Breasts in Middle-Aged Women |date=2020 |pmc=7465213 |last1=Kim |first1=E. Y. |last2=Chang |first2=Y. |last3=Ahn |first3=J. |last4=Yun |first4=J. S. |last5=Park |first5=Y. L. |last6=Park |first6=C. H. |last7=Shin |first7=H. |last8=Ryu |first8=S. |journal=Journal of Clinical Medicine |volume=9 |issue=8 |page=2434 |doi=10.3390/jcm9082434 |doi-access=free |pmid=32751482 }}</ref> The breasts can decrease in size when the levels of circulating estrogen decline. The adipose tissue and milk glands also begin to wither. The breasts can also become enlarged from [[Adverse effect|adverse side effects]] of [[combined oral contraceptive pill]]s. The size of the breasts can also increase and decrease in response to [[body weight|weight]] fluctuations.<ref>{{Cite journal |last1=Wanders |first1=Johanna Olga Pauline |last2=Bakker |first2=Marije Fokje |last3=Veldhuis |first3=Wouter Bernard |last4=Peeters |first4=Petra Huberdina Maria |last5=van Gils |first5=Carla Henrica |date=2015-05-30 |title=The effect of weight change on changes in breast density measures over menopause in a breast cancer screening cohort |journal=Breast Cancer Research |volume=17 |issue=1 |page=74 |doi=10.1186/s13058-015-0583-2 |doi-access=free |issn=1465-542X |pmc=4487974 |pmid=26025139}}</ref> 

Physical changes to the breasts are often recorded in the [[stretch marks]] of the skin envelope; they can serve as historical indicators of the increments and the decrements of the size and volume of a woman's breasts throughout the course of her life.{{Verification needed|date=December 2024|reason=This statement may not correspond to present sources}}

Breast changes during menopause are sometimes treated with [[hormone replacement therapy]].<ref>{{Cite web |date=2023-02-07 |title=What You Should Know About Hormone Therapy and Menopause |url=https://www.cuimc.columbia.edu/news/what-you-should-know-about-hormone-therapy-and-menopause |access-date=2024-12-25 |website=Columbia University Irving Medical Center |language=en}}</ref>

===Cancer===
{{Main|Breast cancer}}
[[File:Black Woman - Breast Self-Exam (1980).jpg|thumb|Woman performing a breast self examination to screen for cancer]]
Breast cancer is a cancer that develops from breast tissue.<ref>{{cite web |title = Breast Cancer |url = http://www.cancer.gov/cancertopics/types/breast |website = NCI |access-date = 29 June 2014 |url-status = live |archive-url = https://web.archive.org/web/20140625232947/http://www.cancer.gov/cancertopics/types/breast |archive-date = 25 June 2014 |date = January 1980 }}</ref> Signs of breast cancer may include a [[Breast lump|lump]] in the breast, a change in breast shape, [[dimpling]] of the skin, [[Milk-rejection sign|milk rejection]], fluid coming from the [[nipple]], a newly inverted nipple, or a red or scaly patch of skin.<ref name=NCI2014Pt>{{cite web |title = Breast Cancer Treatment (PDQ®) |url = http://www.cancer.gov/cancertopics/pdq/treatment/breast/Patient/page1/AllPages |website = NCI |date = 23 May 2014 |access-date = 29 June 2014 |url-status = live |archive-url = https://web.archive.org/web/20140705110404/http://www.cancer.gov/cancertopics/pdq/treatment/breast/Patient/page1/AllPages |archive-date = 5 July 2014 }}</ref> In those with [[Metastatic breast cancer|distant spread of the disease]], there may be [[bone pain]], swollen [[lymph node]]s, [[shortness of breath]], or [[yellow skin]].<ref>{{cite book | vauthors = Saunders C, Jassal S |title = Breast cancer |date = 2009 |publisher = Oxford University Press |location = Oxford |isbn = 978-0-19-955869-8 |page = Chapter 13 |edition = 1. |url = https://books.google.com/books?id=as46WowY_usC&pg=PT123 |url-status = live |archive-url = https://web.archive.org/web/20151025013217/https://books.google.com/books?id=as46WowY_usC&pg=PT123 |archive-date = 25 October 2015 }}</ref>

Risk factors for developing breast cancer include [[obesity]], a [[Sedentary lifestyle|lack of physical exercise]], alcohol consumption, [[hormone replacement therapy]] during [[menopause]], [[ionizing radiation]], an early age at [[Menarche|first menstruation]], having children late in life (or not at all), older age, having a prior history of breast cancer, and a family history of breast cancer.<ref name=NCI2014Pt /><ref name="WCR2014">{{cite book |title = World Cancer Report 2014 |date = 2014 |publisher = World Health Organization |isbn = 978-92-832-0429-9 |pages = Chapter 5.2 }}</ref><ref>{{cite journal | vauthors = Fakhri N, Chad MA, Lahkim M, Houari A, Dehbi H, Belmouden A, El Kadmiri N | title = Risk factors for breast cancer in women: an update review | journal = Medical Oncology | volume = 39 | issue = 12 | article-number = 197 | date = September 2022 | pmid = 36071255 | doi = 10.1007/s12032-022-01804-x | s2cid = 252113509 }}</ref> About five to ten percent of cases are the result of an inherited genetic predisposition,<ref name=NCI2014Pt /> including [[BRCA mutation|''BRCA'' mutations]] among others.<ref name=NCI2014Pt /> Breast cancer most commonly develops in cells from the lining of [[milk ducts]] and the [[lobules]] that supply these ducts with milk.<ref name=NCI2014Pt /> Cancers developing from the ducts are known as [[Invasive ductal carcinoma|ductal carcinomas]], while those developing from lobules are known as [[lobular carcinoma]]s.<ref name=NCI2014Pt /> There are more than 18 other sub-types of breast cancer.<ref name=WCR2014 /> Some, such as [[ductal carcinoma in situ]], develop from [[pre-invasive lesions]].<ref name=WCR2014 /> The diagnosis of breast cancer is confirmed by taking a [[Breast biopsy|biopsy]] of the concerning tissue.<ref name=NCI2014Pt /> Once the diagnosis is made, further tests are carried out to determine if the cancer has spread beyond the breast and which treatments are most likely to be effective.<ref name=NCI2014Pt />

==Breastfeeding==
{{Main|Breastfeeding}}
[[File:Breastfeeding infant.jpg|thumb|upright|A baby breastfeeding]]

The primary function of the breasts, as mammary glands, is the nourishing of an infant with [[breast milk]]. Milk is produced in milk-secreting cells in the alveoli. When the breasts are stimulated by the suckling of her baby, the mother's brain secretes [[oxytocin]]. High levels of oxytocin trigger the contraction of muscle cells surrounding the alveoli, causing milk to flow along the ducts that connect the alveoli to the nipple.<ref name="NCBI Bookshelf 2008">{{cite web | title=The physiological basis of breastfeeding | website=NCBI Bookshelf | date=5 November 2008 | url=https://www.ncbi.nlm.nih.gov/books/NBK148970/ | access-date=13 February 2018 | archive-url=https://web.archive.org/web/20180119051121/https://www.ncbi.nlm.nih.gov/books/NBK148970/ | archive-date=19 January 2018 | url-status=live }}
</ref>

Full-term newborns have an instinct and a need to suck on a nipple, and breastfed babies nurse for both nutrition and for comfort.{{sfn|Lawrence|2016|p=201}}  Breast milk provides all necessary nutrients for the first six months of life, and then remains an important source of nutrition, alongside solid foods, until at least one or two years of age.

== Exercise ==
Biomechanical studies have demonstrated that, depending on the activity and the size of a woman's breast, when she walks or runs braless, her breasts may move up and down by {{convert|4|to|18|cm}} or more, and also oscillate side to side.<ref name=nhsuk/> Researchers have also found that as women's breast size increased, they took part in less physical activity, especially vigorous exercise. Few very-large-breasted women jogged, for example. To avoid exercise-related discomfort and pain, medical experts suggest women wear a well-fitted [[sports bra]] during activity.<ref name=nhsuk>{{cite web |title=How a well-fitted sports bra can reduce breast pain |url=https://www.nhs.uk/live-well/exercise/right-sports-bra-can-reduce-breast-pain/ |website=nhs.uk |access-date=7 March 2019 |language=en |date=30 April 2018}}</ref>

==Clinical significance==
{{Main|Breast disease}}

The breast is susceptible to numerous benign and malignant conditions. The most frequent benign conditions are [[puerperal mastitis]], [[fibrocystic breast changes]] and [[mastalgia]].

[[Lactation]] unrelated to pregnancy is known as [[galactorrhea]]. It can be caused by certain drugs (such as [[antipsychotic]] medications), extreme physical stress, or [[endocrine]] disorders. Lactation in newborns is caused by hormones from the mother that crossed into the baby's bloodstream during pregnancy.

===Breast cancer===
{{Main|Breast cancer}}

Breast cancer is the most common cause of cancer death among women<ref>
{{cite web |author = World Health Organization |date = February 2006 |title = Fact sheet No. 297: Cancer |url =https://www.who.int/mediacentre/factsheets/fs297/en/index.html |access-date = 26 April 2007 |archive-url = https://web.archive.org/web/20140213212322/http://www.who.int/mediacentre/factsheets/fs297/en/index.html |archive-date = 13 February 2014 |url-status = live |author-link = World Health Organization }}</ref> and it is one of the leading causes of death among women. Factors that appear to be implicated in decreasing the risk of breast cancer are regular breast examinations by health care professionals, regular [[mammograms]], [[Breast self-examination|self-examination of breasts]], healthy diet, exercise to decrease excess body fat,<ref>
[http://hms.harvard.edu/public/disease/breast_cancer/7things.html Seven things you should know about breast cancer risk] {{Webarchive|url=https://web.archive.org/web/20100704055600/http://hms.harvard.edu/public/disease/breast_cancer/7things.html |date=4 July 2010 }} Harvard College. Last updated June 2008</ref> and [[breastfeeding]].<ref>{{cite journal|url=https://cebp.aacrjournals.org/content/26/5_Supplement/IA23|journal=Cancer Epidemiology, Biomarkers & Prevention|title=Reducing cancer risk by enabling women to breastfeed|date=May 2017|volume=26|issue=5 Supplement|pages=IA23|doi=10.1158/1538-7755.CARISK16-IA23|access-date=23 September 2019|archive-date=23 September 2019|archive-url=https://web.archive.org/web/20190923170533/https://cebp.aacrjournals.org/content/26/5_Supplement/IA23|url-status=live|last1=Stuebe|first1=Alison M.|url-access=subscription}}</ref>

===Male breasts===
Both females and males develop breasts from the same [[embryology|embryological]] tissues. Anatomically, male breasts do not normally contain lobules and acini that are present in females. In rare instances, it is possible for very few lobules to be present; this makes it possible for some men to develop lobular carcinoma of the breast.<ref>{{Cite journal |last1=Erhan |first1=Yamaç |last2=Zekioglu |first2=Osman |last3=Erhan |first3=Yildiz |date=October 2006 |title=Invasive lobular carcinoma of the male breast |journal=Canadian Journal of Surgery. Journal Canadien de Chirurgie |volume=49 |issue=5 |pages=365–366 |issn=0008-428X |pmc=3207588 |pmid=17152578}}</ref> Normally, males produce lower levels of estrogens and higher levels of [[androgen]]s, namely [[testosterone]], which suppress the effects of estrogens in developing excessive breast tissue. In boys and men, abnormal breast development is manifested as [[gynecomastia]], the consequence of a biochemical imbalance between the normal levels of estrogen and testosterone in the male body.<ref>{{cite book |author = Olson, James Stuart |title = Bathsheba's Breast: Women, Cancer and History |publisher = The Johns Hopkins University Press |location = Baltimore |year = 2002 |page = [https://archive.org/details/bathshebasbreast00olso/page/109 109] |oclc = 186453370 |isbn = 978-0-8018-6936-5 |url = https://archive.org/details/bathshebasbreast00olso/page/109 }}</ref> Around 70% of boys temporarily develop breast tissue during adolescence.<ref name=mgh2010/> The condition usually resolves by itself within two years.<ref name=mgh2010/> When [[male lactation]] occurs, it is considered a symptom of a disorder of the [[pituitary gland]].

===Plastic surgery===
[[File:Mastectomy Procedures.jpg|thumb|upright|Conventional mastectomy ''(top)''; skin sparing mastectomy and [[latissimus dorsi]] myocutaneous flap reconstruction, prior to nipple reconstruction and tattooing ''(bottom)'']]

[[Plastic surgery]] can be performed to [[Breast augmentation|augment]] or [[Breast reduction|reduce]] the size of breasts, or to [[reconstructive surgery|reconstruct]] the breast in cases of deformative disease, such as [[breast cancer]].<ref>{{cite web |url = http://www.sexarchive.info/ATLAS_EN/html/secondary_characteristics.html |title = Secondary sex characteristics |publisher = .hu-berlin.de |access-date = 31 October 2011 |archive-url = https://web.archive.org/web/20130622035035/http://www.sexarchive.info/ATLAS_EN/html/secondary_characteristics.html |archive-date = 22 June 2013 |url-status = live }}
</ref> Breast augmentation and breast lift ([[mastopexy]]) procedures are done only for cosmetic reasons, whereas breast reduction is sometimes medically indicated.<ref name=love_c1/> In cases where a woman's breasts are severely asymmetrical, surgery can be performed to either enlarge the smaller breast, reduce the size of the larger breast, or both.<ref name=love_c1/>

Breast augmentation surgery generally does not interfere with future ability to [[breastfeed]].{{sfn | Lawrence | 2016 | pp= 613–616}} Breast reduction surgery more frequently leads to decreased sensation in the nipple-areola complex, and to low milk supply in women who choose to breastfeed.{{sfn | Lawrence | 2016 | pp= 613–616}} Implants can interfere with [[mammography]] (breast x-ray images).

==Society and culture==
===General===
In [[Saint symbology|Christian iconography]], some works of art depict women with their breasts in their hands or on a platter, signifying that they died as a martyr by having their breasts severed; one example of this is [[Agatha of Sicily|Saint Agatha of Sicily]].<ref>{{cite web |title = St Agatha |url = http://www.catholic.org/saints/saint.php?saint_id=14 |publisher = Catholic Online |access-date = 27 December 2015 |archive-url = https://web.archive.org/web/20160304000129/http://www.catholic.org/saints/saint.php?saint_id=14 |archive-date = 4 March 2016 |url-status = live }}
</ref>

[[File:Bare breasts are our weapons crop.jpg|thumb|upright|[[Femen]] member participating in a protest|left]]

[[Femen]] is a [[feminism|feminist]] activist group which uses [[topless protest]]s as part of their campaigns against [[sex tourism]]<ref name=FEMEN>[http://www.kyivpost.com/news/politics/detail/65379/ Femen wants to move from public exposure to political power] {{Webarchive|url=https://web.archive.org/web/20101207042451/http://www.kyivpost.com/news/politics/detail/65379 |date=7 December 2010 }}, ''[[Kyiv Post]]'' (28 April 2010)</ref><ref name="movements1">{{cite web |url = http://www.movements.org/case-study/entry/ukraines-ladies-of-femen/ |title = Ukraine's Ladies of Femen |publisher = Movements.org |date = 16 August 2011 |access-date = 22 April 2013 |url-status = usurped |archive-url = https://web.archive.org/web/20120414005441/http://www.movements.org/case-study/entry/ukraines-ladies-of-femen |archive-date = 14 April 2012 }}</ref> religious institutions,<ref name=BBCobservOct12>[https://www.bbc.co.uk/news/world-europe-20028797 Ukraine's Femen:Topless protests 'help feminist cause'] {{Webarchive|url=https://web.archive.org/web/20180412230110/http://www.bbc.co.uk/news/world-europe-20028797 |date=12 April 2018 }}, [[BBC News]] (23 October 2012)</ref> [[sexism]], and [[homophobia]].<ref>{{cite news |url = http://www.huffingtonpost.com/2013/04/24/topless-femen-protest-andre-jozef-leonard_n_3146609.html |title = Topless FEMEN Protesters Drench Belgian Archbishop André-Jozef Léonard, Protest Homophobia in Catholic Church (PHOTOS) |work = The Huffington Post |access-date = 23 March 2015 |date = 24 April 2013 |archive-url = https://web.archive.org/web/20150416042913/http://www.huffingtonpost.com/2013/04/24/topless-femen-protest-andre-jozef-leonard_n_3146609.html |archive-date = 16 April 2015 |url-status = live }}</ref> Femen activists have been regularly detained by police in response to their protests.<ref name=BBCTunis>[https://www.bbc.co.uk/news/world-africa-22881163 Femen activists jailed in Tunisia for topless protest] {{Webarchive|url=https://web.archive.org/web/20180827210121/https://www.bbc.co.uk/news/world-africa-22881163 |date=27 August 2018 }}, [[BBC News]] (12 June 2013)</ref>

There is a long history of female breasts being used by comedians as a subject for comedy fodder (e.g., British comic [[Benny Hill|Benny Hill's]] burlesque/slapstick routines).<ref name="thedailybeast.com" />

===Art history===
In European pre-historic societies, sculptures of female figures with pronounced or highly exaggerated breasts were common. A typical example is the so-called [[Venus of Willendorf]], one of many [[Paleolithic]] [[Venus figurines]] with ample hips and bosom. Artifacts such as bowls, rock carvings and sacred statues with breasts have been recorded from 15,000&nbsp;BC up to late antiquity all across Europe, North Africa and the Middle East.

Many female deities representing love and fertility were associated with breasts and breast milk. Figures of the Phoenician goddess [[Astarte]] were represented as pillars studded with breasts. [[Isis]], an Egyptian goddess who represented, among many other things, ideal motherhood, was often portrayed as suckling [[pharaohs]], thereby confirming their divine status as rulers. Even certain male deities representing regeneration and fertility were occasionally depicted with breast-like appendices, such as the river god [[Hapi (Nile god)|Hapy]] who was considered to be responsible for the annual overflowing of the [[Nile]].

[[File:Θεά των Όφεων 6393 (cropped).JPG|thumb|upright|A [[Minoan snake goddess figurines|Cretan snake goddess]] from the [[Minoan civilization]], {{circa|1600}}&nbsp;BC]]

Female breasts were also prominent in [[Minoan art]] in the form of the famous [[Snake Goddess]] statuettes, and a few other pieces, though most female breasts are covered. In [[Ancient Greece]] there were several cults worshipping the "Kourotrophos", the suckling mother, represented by goddesses such as [[Gaia (mythology)|Gaia]], [[Hera]] and [[Artemis]]. The worship of deities symbolized by the female breast in Greece became less common during the first millennium. The popular adoration of female goddesses decreased significantly during the rise of the Greek city states, a legacy which was passed on to the later [[Roman Empire]].<ref>Yalom (1998) pp. 9–16; see Eva Keuls (1993), ''Reign of the Phallus: Sexual Politics in Ancient Athens'' for a detailed study of male-dominant rule in ancient Greece.</ref>

During the middle of the first millennium BC, Greek culture experienced a gradual change in the perception of female breasts. Women in art were covered in clothing from the neck down, including female goddesses like [[Athena]], the patron of Athens who represented heroic endeavor. There were exceptions: [[Aphrodite]], the goddess of love, was more frequently portrayed fully nude, though in postures that were intended to portray shyness or modesty, a portrayal that has been compared to modern [[Pin-up|pin ups]] by historian [[Marilyn Yalom]].<ref>Yalom (1998), p. 18.</ref> Although nude men were depicted standing upright, most depictions of female nudity in Greek art occurred "usually with drapery near at hand and with a forward-bending, self-protecting posture".<ref>Hollander (1993), p. 6.</ref> A popular legend at the time was of the [[Amazons]], a tribe of fierce female warriors who socialized with men only for procreation and even removed one breast to become better warriors (the idea being that the right breast would interfere with the operation of a bow and arrow). The legend was a popular motif in art during Greek and Roman antiquity and served as an antithetical cautionary tale.
[[File:Beauty revealed.jpg|thumb|''[[Beauty Revealed]]'', 1828 self-portrait by the American artist [[Sarah Goodridge]]]]

===Body image===
Many women regard their breasts as important to their [[sexual attractiveness]], as a sign of [[femininity]] that is important to their [[Self-concept|sense of self]]. A woman with smaller breasts may regard her breasts as less attractive.<ref>Koff, E., Benavage, A. Breast Size Perception and Satisfaction, Body Image, and Psychological Functioning in Caucasian and Asian American College Women. Sex Roles 38, 655–673 (1998). https://doi.org/10.1023/A:1018802928210 {{Webarchive|url=https://web.archive.org/web/20180604135059/https://link.springer.com/article/10.1023/A:1018802928210 |date=4 June 2018 }}</ref>

===Clothing===
{{See also|Bra|List of bra designs|Cleavage (breasts)|Toplessness|Modesty|Naturism|Exhibitionism}}
[[File:Namibie Himba 0716a.jpg|thumb|left|upright|A bare-breasted [[Himba people|Himba]] woman of northern Namibia wears a traditional headdress and skirt.]]
Because breasts are mostly fatty tissue, their shape can—within limits—be molded by clothing, such as [[foundation garment]]s. [[Bra]]s are commonly worn by about 90% of Western women,<ref>{{cite web |url = http://www.1stbras.com/bra-cup-sizes.php |archive-url = https://web.archive.org/web/20160308210937/http://www.1stbras.com/bra-cup-sizes.php |url-status = usurped |archive-date = 8 March 2016 |title = Bra Cup Sizes—getting fitted with the right size |publisher = 1stbras.com |access-date = 11 May 2010 }}</ref><ref>{{cite web |url = http://www.liv.com/right_bra.php |archive-url = https://web.archive.org/web/20090328083521/http://www.liv.com/right_bra.php |archive-date = 28 March 2009 |title = The Right Bra |publisher = Liv.com |access-date = 11 May 2010 }}</ref><ref>{{cite news |url = https://www.independent.co.uk/news/uk/this-britain/breast-supporting-act-a-century-of-the-bra-5334510.html |title = Breast supporting act: a century of the bra |date = 15 August 2007 |publisher = The Independent UK |access-date = 11 May 2010 |location = London |archive-url = https://web.archive.org/web/20160305101134/http://www.independent.co.uk/news/uk/this-britain/breast-supporting-act-a-century-of-the-bra-5334510.html |archive-date = 5 March 2016 |url-status = live }}</ref> and are often worn for support.<ref>{{cite journal |pmc = 2275741 |pmid = 18339205 |doi = 10.1186/1746-1340-16-1 |volume = 16 |title = Breast size, bra fit and thoracic pain in young women: a correlational study |year = 2008 |journal = Chiropr Osteopat |article-number = 1 |last1 = Wood |first1 = K |last2 = Cameron |first2 = M |last3 = Fitzgerald |first3 = K |doi-access = free }}</ref> The [[social norm]] in most [[Western culture]]s is to cover breasts in public, though the extent of coverage varies depending on the social context. Some religions ascribe a special status to the female breast, either in formal teachings or through symbolism.<ref>{{cite journal |title=Worshipping Breasts in the Maternal Landscape of India |journal=South Asian Studies |date=27 October 2015 |volume=31 |issue=2015 |doi=10.1080/02666030.2015.1094209 |url=https://www.tandfonline.com/doi/full/10.1080/02666030.2015.1094209 |access-date=30 September 2020 |last1=Bohidar |first1=Anannya |pages=247–253 |s2cid=194282633 |archive-date=2 January 2021 |archive-url=https://web.archive.org/web/20210102165529/https://www.tandfonline.com/doi/full/10.1080/02666030.2015.1094209 |url-status=live |url-access=subscription }}</ref> [[Islam]] forbids free women from exposing their breasts in public.

Many cultures, including Western cultures in North America, associate breasts with sexuality and tend to regard bare breasts as [[modesty|immodest]] or [[decency|indecent]]. In some cultures, like the [[Himba people|Himba]] in northern [[Namibia]], bare-breasted women are normal. In some African cultures, for example, the [[thigh]] is regarded as highly sexualized and never exposed in public, but breast exposure is not taboo. In a few [[Western world|Western countries]] and regions female [[toplessness]] at a beach is acceptable, although it may not be acceptable in the town center.<ref name=":3">{{Cite web |date=2024-10-09 |title=Topless Beaches In Europe: Etiquette, Culture, And What To Expect [Updated On 2024] |url=https://travelpander.com/are-all-beaches-in-europ-topless/ |access-date=2024-12-25 |language=en-US}}</ref>

Social attitudes and laws regarding [[breastfeeding in public]] vary widely. In many countries, breastfeeding in public is common, legally protected, and generally not regarded as an issue. However, even though the practice may be legal or socially accepted, some mothers may nevertheless be reluctant to expose a breast in public to breastfeed<ref>{{cite journal|doi=10.1186/1746-4358-3-11|title=Got milk? Not in public!|pmid=18680578|year=2008|last1=Wolf|first1=J.H.|volume=3|issue=1|page=11|pmc=2518137|journal=International Breastfeeding Journal |doi-access=free }}</ref><ref name=Vance_2005>{{cite journal | last = Vance | first = Melissa R. | title = Breastfeeding Legislation in the United States: A General Overview and Implications for Helping Mothers | journal = LEAVEN | volume = 41 | issue = 3 | pages = 51–54 | date = June–July 2005 | url = http://www.llli.org/llleaderweb/LV/LVJunJul05p51.html | archive-url = https://web.archive.org/web/20070331220518/http://www.llli.org/llleaderweb/LV/LVJunJul05p51.html | archive-date = 31 March 2007}}</ref> due to actual or potential objections by other people, negative comments, or harassment.<ref name=Jordan_2002>{{cite book|editor-last=Jordan|editor-first=Tim|editor-last2=Pile|editor-first2=Steve|title=Social Change|page=[https://archive.org/details/socialchange0000unse/page/233 233]|publisher=Blackwell|year=2002|isbn=978-0-631-23311-4|url=https://archive.org/details/socialchange0000unse/page/233}}</ref> It is estimated that around 63% of mothers across the world have publicly breast-fed.<ref>{{Cite book|title = Breast Feeding With Confidence|last = Cox|first = Sue|publisher = Meadowbrook Press|year = 2002|isbn = 0-684-04005-0|location = United States|url-access = registration|url = https://archive.org/details/breastfeedingwit00suec}}</ref> Bare-breasted women are legal and culturally acceptable at public beaches in Australia and much of Europe.<ref>{{Cite journal |last=Bennett |first=Theodore |title=Clothing Optional?: Nudity and the Law of the Australian Beach |url=https://doaj.org/article/3c5619e831254faca2c5e8cc6f9a617b |journal=Bond Law Review |date=2019 |volume=31 |doi=10.53300/001c.10864 |language=en |issn=2202-4824|doi-access=free }}</ref><ref name=":3" /> Filmmaker [[Lina Esco]] made a film entitled ''[[Free the Nipple (film)|Free the Nipple]]'', which is about "...laws against female toplessness or restrictions on images of female, but not male, nipples", which Esco states is an example of [[sexism]] in society.<ref name="thedailybeast.com">{{cite news |url = http://www.thedailybeast.com/articles/2014/09/09/women-it-s-time-to-reclaim-our-breasts.html |title = Women, It's Time to Reclaim Our Breasts |first = Emily |last = Shire |date = 9 September 2014 |newspaper = The Daily Beast |access-date = 11 December 2016 |archive-url = https://web.archive.org/web/20161101085547/http://www.thedailybeast.com/articles/2014/09/09/women-it-s-time-to-reclaim-our-breasts.html |archive-date = 1 November 2016 |url-status = live }}</ref>

[[Breast binding]], also known as chest binding, is the flattening and hiding of breasts with constrictive materials such as cloth strips or purpose-built [[undergarment]]s. Binders may also be used as alternatives to [[bra]]s or for reasons of propriety. People who bind include women, [[trans man|trans men]], [[non-binary gender|non-binary]] people, and [[cisgender]] men with gynecomastia.

===Sexual characteristic===
{{See also|Mammary intercourse|Breast fetishism|Stimulation of nipples}}

In some cultures, breasts play a role in [[human sexual activity]]. Breasts and especially the nipples are among the various human [[erogenous zone]]s. They are sensitive to the touch as they have many nerve endings; and it is common to press or [[massage]] them with hands or [[stimulation of nipples|orally]] before or during sexual activity. During [[sexual arousal]], breast size increases, [[vein|venous]] patterns across the breasts become more visible, and nipples harden.{{Citation needed|date=December 2024}} Compared to other primates, human breasts are proportionately large throughout adult females' lives. Some writers have suggested that they may have evolved as a visual signal of sexual maturity and fertility.<ref>{{cite journal |author = Anders Pape Møller |title = Breast asymmetry, sexual selection, and human reproductive success |journal = Ethology and Sociobiology |year = 1995 |volume = 16 |issue = 3 |pages = 207–219 |doi = 10.1016/0162-3095(95)00002-3 |display-authors = 1 |last2 = Soler |first2 = M |last3 = Thornhill |first3 = R }}</ref> In ''[[Patterns of Sexual Behavior]]'', a 1951 analysis of 191 traditional cultures, the researchers noted that stimulation of the female breast by a male sexual partner "seemed absent in all subhuman forms, although it is common among the members of many different human societies."<ref>{{Cite book |last=Clellan S. Ford and Frank A. Beach |url=http://archive.org/details/patternsofsexual0000clel_d2x3 |title=Patterns of Sexual Behaviour |date=1965 |others=Internet Archive |page=70}}</ref>

Many people regard bare female breasts to be aesthetically pleasing or [[erotic]], and they can elicit heightened [[sexual desire]]s in men in many cultures. In the [[History of India|ancient Indian]] work the ''[[Kama Sutra]]'', light scratching of the breasts with nails and biting with teeth are considered erotic.<ref>{{cite web |url = http://www.sacred-texts.com/sex/kama/index.htm |title = Sir Richard Burton's English translation of Kama Sutra |publisher = Sacred-texts.com |access-date = 31 October 2011 |archive-url = https://web.archive.org/web/20100102051149/http://sacred-texts.com/sex/kama/index.htm |archive-date = 2 January 2010 |url-status = live }}</ref> Some people show a [[sexual interest]] in female breasts distinct from that of the person, which may be regarded as a [[breast fetish]].<ref>Hickey, Eric W. (2003). Encyclopaedia of Murder and Violent Crime. Sage Publications Inc. {{ISBN|978-0-7619-2437-1}}</ref> A number of Western fashions include clothing which accentuate the breasts, such as the use of [[push-up bra]]s and [[decollete]] (plunging neckline) gowns and blouses which show [[cleavage (breasts)|cleavage]]. While U.S. culture prefers breasts that are youthful and upright, some cultures venerate women with drooping breasts, indicating mothering and the wisdom of experience.<ref>{{cite book |last = Burns-Ardolino |first = Wendy |title = Jiggle: (Re)shaping American women |year = 2007 |publisher = Lexington Books |location = Lanham, MD |isbn = 978-0-7391-1299-1 |page = 31 }}</ref>

Research conducted at the [[Victoria University of Wellington]] showed that breasts are often the first thing men look at, and for a longer time than other body parts.<ref name=ASB>{{cite journal |last1 = Dixson |first1 = BJ |last2 = Grimshaw |first2 = GM |last3 = Linklater |first3 = WL |last4 = Dixson |first4 = AF |title = Eye-tracking of men's preferences for waist-to-hip ratio and breast size of women |journal = [[Archives of Sexual Behavior]] |volume = 40 |issue = 1 |pages = 43–50 |publisher = [[International Academy of Sex Research]] |date = February 2011 |doi = 10.1007/s10508-009-9523-5 |pmid = 19688590 |s2cid = 4997497 }}</ref> The writers of the study had initially speculated that the reason for this is due to [[endocrinology]] with larger breasts indicating higher levels of estrogen and a sign of greater fertility,<ref name=ASB /><ref name=BBC>{{cite news |url = https://news.bbc.co.uk/1/hi/health/3682657.stm |title = Hourglass figure fertility link |work = BBC News |date = 4 May 2004 |access-date = 31 October 2011 |archive-url = https://web.archive.org/web/20111011122830/http://news.bbc.co.uk/2/hi/health/3682657.stm |archive-date = 11 October 2011 |url-status = live }}</ref> but the researchers said that "Men may be looking more often at the breasts because they are simply aesthetically pleasing, regardless of the size."<ref name=ASB />

Some women report achieving an [[orgasm]] from nipple stimulation, but this is rare.<ref name="Kinsey">{{cite book |author1 = Alfred C. Kinsey |author2 = Wardell B. Pomeroy |author3 = Clyde E. Martin |author4 = Paul H. Gebhard |title = Sexual Behavior in the Human Female |publisher = [[Indiana University Press]] |isbn = 0-253-01924-9 |page = 587 |date = 1998 |access-date = 12 August 2017 |url = https://books.google.com/books?id=JHWHCgAAQBAJ&pg=PA587 |quote = There are some females who appear to find no erotic satisfaction in having their breasts manipulated; perhaps half of them derive some distinct satisfaction, but not more than a very small percentage ever respond intensely enough to reach orgasm as a result of such stimulation (Chapter 5). [...] Records of females reaching orgasm from breast stimulation alone are rare. }}</ref><ref name="Boston">{{cite book |author = Boston Women's Health Book Collective |title = The New Our Bodies, Ourselves: A Book by and for Women |publisher = [[Simon & Schuster]] |isbn = 0-684-82352-7 |page = 575 |date = 1996 |access-date = 12 August 2017 |url = https://books.google.com/books?id=JFI4AQAAIAAJ |quote = A few women can even experience orgasm from breast stimulation alone. |archive-date = 24 December 2020 |archive-url = https://web.archive.org/web/20201224162656/https://books.google.com/books?id=JFI4AQAAIAAJ |url-status = live }}</ref> Research suggests that the orgasms are genital orgasms, and may also be directly linked to "the genital area of the brain". In these cases, it seems that sensation from the nipples travels to the same part of the brain as sensations from the vagina, clitoris and cervix. Nipple stimulation may trigger uterine contractions, which then produce a sensation in the genital area of the brain.<ref name="Smith">{{cite book |author = Merril D. Smith |title = Cultural Encyclopedia of the Breast |publisher = [[Rowman & Littlefield]] |isbn = 978-0-7591-2332-8 |page = 71 |date = 2014 |access-date = 12 August 2017 |url = https://books.google.com/books?id=qrCCBAAAQBAJ&pg=PA71 }}</ref><ref name="Lehmiller">{{cite book |author = Justin J. Lehmiller |title = The Psychology of Human Sexuality |publisher = [[John Wiley & Sons]] |isbn = 978-1-118-35132-1 |page = 120 |date = 2013 |access-date = 12 August 2017 |url = https://books.google.com/books?id=pQRgAgAAQBAJ&pg=PT120 |archive-date = 23 February 2019 |archive-url = https://web.archive.org/web/20190223070048/https://books.google.com/books?id=pQRgAgAAQBAJ&pg=PT120 |url-status = live }}</ref><ref name="Komisaruk">{{Cite journal|author1-link=Barry Komisaruk|author1 = Komisaruk, B. R. |author2 = Wise, N. |author3 = Frangos, E. |author4 = Liu, W.C. |author5 = Allen, K. |author6 = Brody, S. |title = Women's Clitoris, Vagina, and Cervix Mapped on the Sensory Cortex: fMRI Evidence, Surprise finding in response to nipple stimulation |journal = [[The Journal of Sexual Medicine]] |year = 2011 |doi = 10.1111/j.1743-6109.2011.02388.x |volume = 8 |issue = 10 |pages = 2822–30 |pmid = 21797981 |pmc = 3186818}}
*{{cite news |author=Stephanie Pappas |date=5 August 2011 |title=Surprise finding in response to nipple stimulation |work=CBS News |url=http://www.cbsnews.com/news/surprise-finding-in-response-to-nipple-stimulation/  |access-date=12 August 2017 |archive-url=https://web.archive.org/web/20160701074316/http://www.cbsnews.com/news/surprise-finding-in-response-to-nipple-stimulation/ |archive-date=1 July 2016 |url-status=live}}</ref>

===Anthropomorphic geography===
{{Main|Breast-shaped hill}}

There are many mountains named after the breast because they resemble it in appearance and so are objects of religious and ancestral veneration as a fertility symbol and of well-being. In Asia, there was "Breast Mountain", which had a cave where the [[Buddhist monk]] [[Bodhidharma]] (Da Mo) spent much time in [[meditation]].<ref>{{cite web |url=http://www.usashaolintemple.org/chanbuddhism-history/ |title=The Story of Bodhidharma |publisher=Usashaolintemple.org |access-date=31 October 2011 |archive-url=https://web.archive.org/web/20111130054841/http://www.usashaolintemple.org/chanbuddhism-history/ |archive-date=30 November 2011 |url-status=live }}</ref> Other such breast mountains are [[Mount Elgon]] on the [[Uganda]]–[[Kenya]] border; {{lang|gd|[[Lochnagar|Beinn Chìochan]]|italic=no}} and the [[Maiden Paps, Caithness|Maiden Paps]] in Scotland; the {{lang|tl|[[Mount Tagapo|Bundok ng Susong Dalaga]]|italic=no}} ('Maiden's breast mountains') in [[Talim Island]], Philippines, the twin hills known as the [[Paps of Anu]] ({{lang|ga|Dá Chích Anann}} or 'the breasts of [[Anu (goddess)|Anu]]'), near [[Killarney]] in Ireland; the 2,086&nbsp;m high {{Lang|es|Tetica de Bacares|italic=no}} or {{lang|es|La Tetica|italic=no}} in the {{lang|es|[[Sierra de Los Filabres]]|italic=no}}, Spain; {{lang|th-Latn|[[Khao Nom Sao]]|italic=no}} in Thailand, {{lang|es|[[Cerro Las Tetas]]|italic=no}} in [[Puerto Rico]]; and the Breasts of Aphrodite in [[Mykonos]], among many others. In the United States, the [[Teton Range]] is named after the French word for 'nipple'.<ref>{{cite web |url=https://www.nps.gov/parkhistory/online_books/grte/grte_geology/sec1.htm |title=Creation of the Teton Landscape: The Geologic Story of Grand Teton National Park (The Story Begins) |publisher=[[National Park Service]] |date=19 January 2007 |access-date=23 September 2011 |archive-url=https://web.archive.org/web/20150419054617/http://www.nps.gov/parkhistory/online_books/grte/grte_geology/sec1.htm |archive-date=19 April 2015 |url-status=live }}</ref>

==Measurement==
{{Main|Breast measurement}}

The [[breast development|maturation]] and [[breast size|size]] of the breasts can be measured by a variety of different methods. These include [[Tanner staging]], [[bra cup size]], [[breast volume]], [[breast–chest difference]], the [[breast unit]], [[breast hemicircumference]], and [[breast circumference]], among other measures.

== See also ==
{{Portal|Medicine|Human sexuality}}
* [[Udder]]
==Notes==
{{Notelist}}

==References==
{{Reflist}}

=== Bibliography ===
* {{cite book |last = Hollander |first = Anne |title = Seeing through clothes |publisher = University of California Press |location = Berkeley |year = 1993 |isbn = 978-0-520-08231-1 }}
* [[Desmond Morris|Morris, Desmond]] ''The Naked Ape: a zoologist's study of the human animal'' Bantam Books, Canada. 1967
* {{cite book |last = Yalom |first = Marilyn |title = A history of the breast |publisher = Pandora |location = London |year = 1998 |isbn = 978-0-86358-400-8 }}
* {{cite book |last = Venes |first = Donald |title = Taber's cyclopedic medical dictionary |publisher = F.A. Davis |location = Philadelphia |year = 2013 |isbn = 978-0-8036-2977-6 }}
* {{cite book | last=Lawrence | first=Ruth | title=Breastfeeding: a guide for the medical profession, 8th edition | publisher=Elsevier | location=Philadelphia, PA | year=2016 | isbn=978-0-323-35776-0 }}

==External links==
{{Wiktionary|breast|breasts}}
{{Commons category|Breasts}}
{{Wikiquote}}
{{Wikibooks|Radiation Oncology/Breast}}
{{Wikisource|1911 Encyclopædia Britannica/Breast}}
* {{cite web |archive-url = https://web.archive.org/web/20111202170751/http://www.nyu.edu/fas/ihpk/CultureMatters/Mascia-Lees.htm |title = Are Women Evolutionary Sex Objects?: Why Women Have Breasts |archive-date = 2 December 2011 |url = http://www.nyu.edu/fas/ihpk/CultureMatters/Mascia-Lees.htm }}

{{Human regional anatomy}}
{{Breast anatomy}}
{{Disorders of the breast}}
{{Sex}}
{{Authority control}}

[[Category:Breastfeeding]]
[[Category:Breast| ]]
[[Category:Human sexuality]]
[[Category:Human physiology]]
[[Category:Anatomy]]
[[Category:Human body]]
[[Category:Health]]