Editing Body odor (section)

===Animals===
In many animals, body odor plays an important survival function. Strong body odor can be a [[warning signal]] for predators to stay away (such as [[North American porcupine#Stench|porcupine stink]]), or it can also be a signal that the prey animal is [[unpalatable]].<ref>{{cite book | vauthors = Ruxton GD, Allen WL, Sherratt TN, Speed MP |title=Avoiding Attack: The Evolutionary Ecology of Crypsis, Aposematism, and Mimicry |year=2018 |publisher=Oxford University Press |isbn=978-0-19-186849-8 }}{{page needed|date=September 2020}}</ref> For example, some animal species that feign death to survive (like [[opossum]]s), in this state produce a strong body odor to deceive a predator that the prey animal has been dead for a long time and is already in the advanced stage of decomposing. Some animals with strong body odor are rarely attacked by most predators, although they can still be killed and eaten by birds of prey, which are tolerant of carrion odors.{{citation needed|date=March 2022}}

Body odor is an important feature of animal physiology. It plays a different role in different animal species. For example, in some predator species that hunt by stalking (such as big and small [[cat]]s), the absence of body odor is important, and they spend plenty of time and energy to keep their body free of odor. For other predators, such as those that hunt by visually locating prey and running for long distances after it (such as [[dog]]s and [[Gray wolf|wolves]]), the absence of body odor is not critical. In most animals, body odor intensifies in moments of stress and danger.<ref>{{cite journal | vauthors = Takahashi LK | title = Olfactory systems and neural circuits that modulate predator odor fear | journal = Frontiers in Behavioral Neuroscience | volume = 8 | pages = 72 | date = 11 March 2014 | pmid = 24653685 | pmc = 3949219 | doi = 10.3389/fnbeh.2014.00072 | doi-access = free }}</ref>

====Humans====
In humans, body odor serves as a means of chemosensory signal communication between members of the species. These signals are called [[pheromone]]s and they can be transmitted through a variety of mediums. The most common way that human pheromones are transmitted is through bodily fluids. Human pheromones are contained in sweat, semen, vaginal secretions, breast milk, and urine.<ref name="lund-4" /> The signals carried in these fluids serve a range of functions from reproductive signaling to infant socialization.<ref name="Damon_2021">{{cite journal | vauthors = Damon F, Mezrai N, Magnier L, Leleu A, Durand K, Schaal B | title = Olfaction in the Multisensory Processing of Faces: A Narrative Review of the Influence of Human Body Odors | journal = Frontiers in Psychology | volume = 12 | pages = 750944 | date = 2021-10-05 | pmid = 34675855 | pmc = 8523678 | doi = 10.3389/fpsyg.2021.750944 | doi-access = free }}</ref> Each person produces a unique spread of pheromones that can be identified by others.<ref name="Grammer_2005">{{cite journal | vauthors = Grammer K, Fink B, Neave N | title = Human pheromones and sexual attraction | journal = European Journal of Obstetrics, Gynecology, and Reproductive Biology | volume = 118 | issue = 2 | pages = 135–142 | date = February 2005 | pmid = 15653193 | doi = 10.1016/j.ejogrb.2004.08.010 }}</ref> This differentiation allows the formation of sexual attraction and kinship ties to occur.<ref name="Grammer_2005" /><ref name="Porter_1985">{{cite journal | vauthors = Porter RH, Cernoch JM, Balogh RD | title = Odor signatures and kin recognition | journal = Physiology & Behavior | volume = 34 | issue = 3 | pages = 445–448 | date = March 1985 | pmid = 4011726 | doi = 10.1016/0031-9384(85)90210-0 | s2cid = 42316168 }}</ref>

[[Sebaceous]] and [[apocrine gland]]s become active at [[puberty]]. This, as well as many apocrine glands being close to the sex organs, points to a role related to mating.<ref name="Oxford2007" /> Sebaceous glands line the human skin while apocrine glands are located around body hairs.<ref name="lund-4" /> Compared to other primates, humans have extensive axillary hair and have many odor producing sources, in particular many apocrine glands.<ref name="AEP" /> In humans, the apocrine glands have the ability to secrete [[pheromone]]s. These steroid compounds are produced within the peroxisomes of the apocrine glands by enzymes such as mevalonate kinases.<ref>{{cite journal | vauthors = Rothardt G, Beier K | title = Peroxisomes in the apocrine sweat glands of the human axilla and their putative role in pheromone production | journal = Cellular and Molecular Life Sciences | volume = 58 | issue = 9 | pages = 1344–1349 | date = August 2001 | pmid = 11577991 | doi = 10.1007/PL00000946 | s2cid = 28790000 | pmc = 11337405 }}</ref>

==== Sexual selection ====
Pheromones are a factor seen in the mating selection and reproduction in humans. In women, the sense of olfaction is strongest around the time of [[ovulation]], significantly stronger than during other phases of the [[menstrual cycle]] and also stronger than the sense in males.<ref>{{harvnb|Lundström|Olsson|2010|ps=:"In addition, the impact that biological factors have on our percept of body odors has recently been indirectly demonstrated by several experiments. Our percept of body odors is dependent on the sexual orientations of both the donor and the perceiver (Martins et al., 2005), and heterosexual women's percept of men's body odor varies over their menstrual cycle (Roberts et al., 2004)."}}</ref><ref>{{cite journal | vauthors = Navarrete-Palacios E, Hudson R, Reyes-Guerrero G, Guevara-Guzmán R | title = Lower olfactory threshold during the ovulatory phase of the menstrual cycle | journal = Biological Psychology | volume = 63 | issue = 3 | pages = 269–279 | date = July 2003 | pmid = 12853171 | doi = 10.1016/s0301-0511(03)00076-0 | s2cid = 46065468 | doi-access = free }}</ref> Pheromones can be used to deliver information about the [[major histocompatibility complex]] (MHC).<ref name="Grammer_2005"/>   The MHC in humans is referred to as the [[Human leukocyte antigen|Human Leukocyte Antigen]] (HLA).<ref name="Kromer_2016">{{cite journal | vauthors = Kromer J, Hummel T, Pietrowski D, Giani AS, Sauter J, Ehninger G, Schmidt AH, Croy I | title = Influence of HLA on human partnership and sexual satisfaction | journal = Scientific Reports | volume = 6 | pages = 32550 | date = August 2016 | pmid = 27578547 | pmc = 5006172 | doi = 10.1038/srep32550 | bibcode = 2016NatSR...632550K }}</ref> Each type has a unique scent profile that can be utilized during the mating selection process. When selecting mates, women tend to be attracted to those that have different HLA-types than their own.<ref name="Grammer_2005" /><ref name="Kromer_2016" />  This is thought to increase the strength of the family unit and increase the chances of survival for potential offspring.<ref name="Grammer_2005" />

Studies have suggested that people might be using odor cues associated with the immune system to select mates. Using a brain-imaging technique, Swedish researchers have shown that [[homosexuality|homosexual]] and [[heterosexuality|heterosexual]] males' brains respond in different ways to two odors that may be involved in sexual arousal, and that homosexual men respond in the same way as heterosexual women, though it could not be determined whether this was cause or effect. When the study was expanded to include lesbian women, the results were consistent with previous findings – meaning that lesbian women were not as responsive to male-identified odors, while responding to female odors in a similar way as heterosexual males.<ref>{{cite journal |vauthors=Berglund H, Lindström P, Savic I |date=May 2006 |title=Brain response to putative pheromones in lesbian women |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=103 |issue=21 |pages=8269–8274 |bibcode=2006PNAS..103.8269B |doi=10.1073/pnas.0600331103 |pmc=1570103 |pmid=16705035 |doi-access=free}}</ref> According to the researchers, this research suggests a possible role for human pheromones in the biological basis of [[sexual orientation]].<ref>{{cite news |date=9 May 2005 |title=Gay Men Are Found to Have Different Scent of Attraction |work=The New York Times |url=https://www.nytimes.com/2005/05/09/science/09cnd-smell.html |vauthors=Wade N}}</ref>

==== Kinship communication ====
Humans can olfactorily detect blood-related kin.<ref name="Porter_1985"/> Mothers can identify by body odor their biological children, but not their stepchildren. Preadolescent children can olfactorily detect their full siblings, but not half-siblings or step-siblings, and this might explain [[inbreeding avoidance|incest avoidance]] and the [[Westermarck effect]].<ref>{{cite journal | vauthors = Weisfeld GE, Czilli T, Phillips KA, Gall JA, Lichtman CM | title = Possible olfaction-based mechanisms in human kin recognition and inbreeding avoidance | journal = Journal of Experimental Child Psychology | volume = 85 | issue = 3 | pages = 279–295 | date = July 2003 | pmid = 12810039 | doi = 10.1016/s0022-0965(03)00061-4 }}</ref> Babies can recognize their mothers by smell while mothers, fathers, and other relatives can identify a baby by smell.<ref name="Oxford2007" /> This connection between genetically similar family members is due to the habituation of familial pheromones. In the case of babies and mothers, this chemosensory information is primarily contained within breastmilk and the mother's sweat. When compared to that of strangers, babies are observed to have stronger neural connections with their mothers.<ref name="Endevelt-Shapira_2021">{{cite journal | vauthors = Endevelt-Shapira Y, Djalovski A, Dumas G, Feldman R | title = Maternal chemosignals enhance infant-adult brain-to-brain synchrony | journal = Science Advances | volume = 7 | issue = 50 | pages = eabg6867 | date = December 2021 | pmid = 34890230 | pmc = 8664266 | doi = 10.1126/sciadv.abg6867 | bibcode = 2021SciA....7.6867E }}</ref> This strengthened neurological connection allows for the biological development and socialization of the infant by their mother. Using these connections, the mother transmits olfactory signals to the infant which are then perceived and integrated.<ref name="Endevelt-Shapira_2021" />

In terms of biological functioning, olfactory signaling allows for functional [[breastfeeding]] to occur. In cases of effective latching, breastfed infants are able to locate their mother's nipples for feeding using the sensory information enclosed in their mother's body odor.<ref name="Varendi_1994">{{cite journal | vauthors = Varendi H, Porter RH, Winberg J | title = Does the newborn baby find the nipple by smell? | language = English | journal = Lancet | volume = 344 | issue = 8928 | pages = 989–990 | date = October 1994 | pmid = 7934434 | doi = 10.1016/S0140-6736(94)91645-4 | s2cid = 35029502 }}</ref> While no specific human breast pheromones have been identified, studies compare the communication to that of the rabbit mammary pheromone 2MB2.<ref>{{Citation | vauthors = Schaal B |title=Pheromones for Newborns |date=2014 |url=http://www.ncbi.nlm.nih.gov/books/NBK200997/ |work=Neurobiology of Chemical Communication | veditors = Mucignat-Caretta C |series=Frontiers in Neuroscience |place=Boca Raton (FL) |publisher=CRC Press/Taylor & Francis |isbn=978-1-4665-5341-5 |pmid=24830031 |access-date=2022-11-27}}</ref><ref>{{Cite web |title=Pheromone From Mother's Milk May Rapidly Promote Learning In Newborn Mammals |url=https://www.sciencedaily.com/releases/2006/10/061010022813.htm |access-date=2022-11-27 |website=ScienceDaily |language=en}}</ref> The perception and integration of these signals is an evolutionary response that allows newborns to locate their source of nutrition. Signaling contains a level of precision that allows babies to differentiate their mother's breasts from that of other women. Once the baby recognizes the familiar olfactory signal, the behavioral response of latching follows. Over time the infant becomes habituated to their mother's breast pheromones which increases latch efficiency.<ref name="Varendi_1994" />

Beyond a biological function, a mother's body odor plays a role in developing a baby's social capabilities. The ability of an infant to evaluate the properties of human faces stems from the olfactory cues given from their mother.<ref name="Damon_2021"/> Frequent exposure to the [[pheromone]]s exuded by their mother allows the connection between vision and smell to form in infants.<ref name="Endevelt-Shapira_2021" /> This type of connection is only found between mothers and babies and over time it socializes the ability to recognize the features that distinguish human faces from inanimate objects.<ref name="Damon_2021" />

==== Environmental threats ====
The connection between olfactory and visual cues has also been observed outside of familial relationships. Evolutionarily, body odor has been used to communicate messages about potentially dangerous stimuli in the environment.<ref name="lund-4" />  Body odor produced during particularly stressful situations can produce a cascade of reactions in the brain. Once the olfactory system is activated by a threatening stimuli, heightened activity in the [[amygdala]] and [[Occipital lobe|occipital cortex]] is triggered.<ref>{{cite journal | vauthors = Mujica-Parodi LR, Strey HH, Frederick B, Savoy R, Cox D, Botanov Y, Tolkunov D, Rubin D, Weber J | title = Chemosensory cues to conspecific emotional stress activate amygdala in humans | journal = PLOS ONE | volume = 4 | issue = 7 | pages = e6415 | date = July 2009 | pmid = 19641623 | pmc = 2713432 | doi = 10.1371/journal.pone.0006415 | bibcode = 2009PLoSO...4.6415M | doi-access = free }}</ref><ref name="lund-4" /> This chain reaction serves to help assess the nature of the threat and increase chance of survival.

Humans have few olfactory receptor cells compared to dogs and few functional olfactory receptor genes compared to rats. This is in part due to a reduction of the size of the snout in order to achieve [[depth perception]] as well as other changes related to bipedalism. However, it has been argued that humans may have larger brain areas associated with olfactory perception compared to other species.<ref name=AEP>{{cite book |doi= 10.1093/acprof:oso/9780199586073.003.0020 |chapter=Evolutionary psychology and perfume design |title=Applied Evolutionary Psychology |year=2011 | vauthors = Roberts SC, Havlicek J |pages=330–348 |isbn=978-0-19-958607-3 }}</ref>