Body odor or body odour (BO) is the unique odor secreted by an animal or produced by microorganisms on an animal's outermost surfaces. It is present in all animals, and its intensity can be influenced by many factors (behavioral patterns, survival strategies). Body odor has a strong genetic basis, but it can also be strongly influenced by various factors, such as sex, diet, health, and medication. The body odor of human males plays an important role in human sexual attraction as a powerful indicator of genetic variation (MHC/HLA heterozygosity);
Causes
In humans, the formation of body odors is caused by factors such as diet, sex, health, and medication, but the major contribution comes from bacterial activity on skin gland secretions. In humans, the armpit regions seem more important than the genital region for body odor, which may be related to human bipedalism. The genital and armpit regions also contain springy hairs which help diffuse body odors.
Body odor is influenced by the actions of the skin flora, including members of Corynebacterium, which manufacture enzymes called lipases that break down the lipids in sweat to create smaller molecules like butyric acid. Greater bacteria populations of Corynebacterium jeikeium are found more in the armpits of men, whereas greater population numbers of Staphylococcus haemolyticus are found in the armpits of women. This causes male armpits to give off a rancid/cheese-like smell, whereas female armpits give off a more fruity/onion-like smell. Staphylococcus hominis is also known for producing thioalcohol compounds that contribute to odors. These smaller molecules smell, and give body odor its characteristic aroma. Propionic acid (propanoic acid) is present in many sweat samples. This acid is a breakdown product of some amino acids by propionibacteria, which thrive in the ducts of adolescent and adult sebaceous glands. Because propionic acid is chemically similar to acetic acid, with similar characteristics including odor, body odors may be identified as having a pungent, cheesy and vinegar-like smell although certain people might find it pleasant at lower concentrations. Isovaleric acid (3-methyl butanoic acid) is the other source of body odor as a result of actions of the bacteria Staphylococcus epidermidis, which is also present in several types of strong cheese.
Factors such as food, drink, gut microbiome, and genetics can affect body odor. For example, some animal species that feign death to survive (like opossums), 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.
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 cats), 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 dogs and wolves), the absence of body odor is not critical. In most animals, body odor intensifies in moments of stress and danger.
Humans
In humans, body odor serves as a means of chemosensory signal communication between members of the species. These signals are called pheromones 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. Each person produces a unique spread of pheromones that can be identified by others. This differentiation allows the formation of sexual attraction and kinship ties to occur.
Sebaceous and apocrine glands become active at puberty. This, as well as many apocrine glands being close to the sex organs, points to a role related to mating.
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. Pheromones can be used to deliver information about the major histocompatibility complex (MHC). 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 from their own. According to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation.
Kinship communication
Humans can olfactorily detect blood-related kin. Babies can recognize their mothers by smell while mothers, fathers, and other relatives can identify a baby by smell. 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. While no specific human breast pheromones have been identified, studies compare the communication to that of the rabbit mammary pheromone 2MB2. 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.
Genes affecting body odor
thumb|250px|World map of the distribution of the A allele of the single nucleotide polymorphism rs17822931 in the [[ABCC11|ABCC11 gene. The proportion of A alleles in each population is represented by the white area in each circle.]]
MHC
Body odor is influenced by major histocompatibility complex (MHC) molecules. These are genetically determined and play an important role in immunity of the organism. The vomeronasal organ contains cells sensitive to MHC molecules in a genotype-specific way.
Experiments on animals and volunteers have shown that potential sexual partners tend to be perceived more attractive if their MHC composition is substantially different. Married couples are more different regarding MHC genes than would be expected by chance. This behavior pattern promotes variability of the immune system of individuals in the population, thus making the population more robust against new diseases. Another reason may be to prevent inbreeding.
ABCC11
The ABCC11 gene determines axillary body odor and earwax type. The loss of a functional ABCC11 gene is caused by a 538G>A single-nucleotide polymorphism, resulting in a loss of body odor in people who are specifically homozygous for it. Firstly, it affects apocrine sweat glands by reducing secretion of odorous molecules and its precursors. The lack of ABCC11 function results in a decrease of the odorant compounds 3M2H, HMHA, and 3M3SH via a strongly reduced secretion of the precursor amino-acid conjugates 3M2H–Gln, HMHA–Gln, and Cys–Gly–(S) 3M3SH; and a decrease of the odoriferous steroids androstenone and androstenol, possibly due to the reduced secretion of dehydroepiandrosterone sulfate (DHEAS) and dehydroepiandrosterone (DHEA), thought to be precursors for skin bacterial metabolism leading to the steroids' formation.
Research has indicated a strong association between people with axillary osmidrosis, a condition characterized by axillary odor, and the ABCC11-genotypes GG or GA in comparison to the genotype AA.
! style="text-align:left;"|Ethnic groups
! style="text-align:left;"|Tribes or inhabitants
! style="text-align:left;"|AA
! style="text-align:left;"|GA
! style="text-align:left;"|GG
|-
|Korean ||Daegu city inhabitants ||100% || 0% ||0%
|-
|Chinese ||Northern and southern Han Chinese ||80.8% || 19.2% ||0%
|-
|Mongolian ||Khalkha tribe ||75.9% ||21.7% || 2.4%
|-
|Japanese ||Nagasaki people ||69% ||27.8% || 3.2%
|-
|Thai||Central Thai in Bangkok ||63.3% ||20.4% ||16.3%
|-
|Vietnamese ||People from multiple regions ||53.6% ||39.2% ||7.2%
|-
|Dravidian|| Inhabitants of southern India ||54.0%||17%||29%
|-
|Native American || ||30% ||40% ||30%
|-
|Filipino ||Palawan ||22.9% ||47.9% ||29.2%
|-
|Kazakh || ||20% ||36.7% ||43.3%
|-
|Russian || ||4.5% ||40.2% ||55.3%
|-
|White Americans ||From CEPH families without the French and Venezuelans ||1.2% ||19.5% || 79.3%
|-
|African ||From various sub-Saharan nations ||0% || 8.3% ||91.7%
|-
|African Americans || ||0% ||0% ||100%
|}
{| class="wikitable"
|+Amino-acid conjugates of key human body odorants in sweat samples of panelists with different genotypes, determined by liquid chromatography-mass spectrometry
! style="text-align:left;"|Genotype<br /> ABCC11
! style="text-align:left;"|Sex
! style="text-align:left;"|Ethnic population
! style="text-align:left;"|Age
! style="text-align:left;"|Net weight <br /><small> sweat (g)/2 pads</small>
! style="text-align:left;"|HMHA–Gln<br /><small>(μmol/2 pads)</small>
! style="text-align:left;"|3M2H–Gln<br /><small>(μmol/2 pads)</small>
! style="text-align:left;"|Cys–Gly conjugate
of 3M3SH <small>(μmol/2 pads)</small>
|-
|AA || F ||Chinese || 27 || 2.05 || ND ||ND || ND
|-
|AA || F || Filipino ||33 || 2.02 || ND ||ND ||ND
|-
|AA || F || Korean ||35 ||1.11 || ND ||ND || ND
|- style="background:#efefef; color:black"
|GA || F || Filipino ||31 || 1.47 || 1.23 || 0.17 ||Detectable, < 0.03 μmol
|- style="background:#efefef; color:black"
|GA || F || Thai ||25 || 0.90 ||0.89 || 0.14 ||Detectable, < 0.03 μmol
|- style="background:#efefef; color:black"
|GA || F || German || 25 ||1.64 ||0.54 ||0.10 ||Detectable, < 0.03 μmol
|-
|GG || F ||Filipino ||45 ||1.74 ||0.77 ||0.13 ||Detectable, < 0.03 μmol
|-
|GG || F || German ||28 ||0.71 ||1.30 ||0.19 || 0.041
|-
|GG || F || German ||33 ||1.23 ||1.12 ||0.16 || 0.038
|}
<small>* ND indicates that no detectable peak is found on the [M+H]+ ion trace of the selected analyte at the correct retention time. <br />* HMHA: 3-hydroxy-3-methyl-hexanoic acid; 3M2H: (E)-3-methyl-2-hexenoic acid; 3M3SH: 3-methyl-3-sulfanylhexan-1-ol.</small>
Other factors affecting body odor
Age
As seen in non-human animals such as mice, black-tailed deer, rabbits, otters, and owl monkeys, body odor contains age-related signals that these animals can detect and process. Similarly, humans have been seen to distinguish age-related information from body odor, particularly relating to odors of those of old age. In a study determining if there is a difference between the body odor of individuals of various ages, three groups were studied: those aged 20-30, aged 45-55, and aged 75-95, corresponding to young age, middle-aged, and old age, respectively. This study determined that individuals could distinguish between odors of various ages and group odors of old age, suggesting that there are certain chemical differences in age resulting in "age-dependent odor characteristics".
Another study evaluated the components of body odor in participants aged 26 through 75 using headspace gas chromatography and mass spectroscopy. This study demonstrated that in individuals 40 years or older, 2-Nonenal, an unsaturated aldehyde producing a greasy and grassy odor, was detected in increasing concentrations of those individuals. The detection of increasing amounts of 2-Nonenal in individuals 40 years or older suggested that 2-Nonenal contributes to the deteriorating body odor seen with aging.
Diseases
In mammals, body odor can also be used as a symptom of disease. One's body odor is completely unique to themselves, similar to a fingerprint, and can change due to sexual life, genetics, age and diet. Body odor, however, can be used as an indication for disease. For example, typically, human urine contains 95% water, however, for a person with an abnormal amount of blood sugar, their urine becomes more concentrated with glucose. Therefore, if a person's body odor or urine smells unusually fruity or sweet, that can be a sign of diabetes. Additionally, an ammonia smell that occurs in one's body, urine, or breath could also be an indicator of kidney disease. Typically, the liver converts ammonia to urea because ammonia has a high level of toxicity. The kidneys are responsible for removing waste, such as urea, out from the body. However, if the kidneys are not functioning properly, this urea is kept as ammonia, causing the urine and even one's breath to smell like ammonia. In conclusion, body odor could be used as a helpful indicator of disease, especially when it suddenly deviates from normal.
Alterations
Body odor may be reduced or prevented or even aggravated by using deodorants, antiperspirants, disinfectants, underarm liners, triclosan, special soaps or foams with antiseptic plant extracts such as ribwort and liquorice, chlorophyllin ointments and sprays topically, and chlorophyllin supplements internally. Although body odor is commonly associated with hygiene practices, its presentation can be affected by changes in diet as well as the other factors. Skin spectrophotometry analysis found that males who consumed more fruits and vegetables were significantly associated with more pleasant smelling sweat, which was described as "floral, fruity, sweet and medicinal qualities".
Industry
As many as 90% of Americans and 92% of teenagers use antiperspirants or deodorants. In 2014, the global market for deodorants was estimated at US$13 billion with a compound annual growth rate of 5.62% between 2015 and 2020.
Medical conditions
Osmidrosis or bromhidrosis is defined by a foul odor due to a water-rich environment that supports bacteria, which is caused by an abnormal increase in perspiration (hyperhidrosis).
Treatment
If body odor is affecting a person's quality of life, then seeing a primary care physician may be helpful. A doctor could recommend prescription antiperspirants containing aluminum-chloride. This chemical agent helps temporarily block sweat pores which reduces the amount a person will sweat. Deodorant is another remedy for body odor. It specifically targets odor but will not reduce sweat. Deodorants are usually alcohol-based which fights off bacteria. Most deodorants contain perfumes which also help with masking odor. If someone is experiencing severe body odor, a doctor may recommend a surgical procedure called endoscopic thoracic sympathectomy. This surgery will cut nerves that control sweating. This surgery poses the risk of harming other nerves in the body.
Prevention
Bathing daily with antibacterial soap reduces the amount of bacteria found on the skin. Shaving armpit hair allows for sweat to evaporate more quickly so it won't produce an odor. Applying deodorant or antiperspirant after showering which helps kill bacteria and prevent someone from sweating is helpful.
Trimethylaminuria (TMAU), also known as fish odor syndrome or fish malodor syndrome, is a rare metabolic disorder where trimethylamine is released in the person's sweat, urine, and breath, giving off a strong fishy odor or strong body odor.
See also
- Drug resistance
- Foot odor
- Halitosis (bad breath)
- Old person smell
- Olfactory fatigue
- Pheromone
- Sweat gland