Underarm hair, also known as axillary hair, is the

hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fi ...

in the underarm area (''axilla'').

Development

Underarm or axillary hair goes through four stages of development, driven by weak

androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This in ...

s produced by the adrenal in males and females during

adrenarche Adrenarche is an early stage in sexual maturation that happens in some higher primates and in humans, typically peaks at around 20 years of age, and is involved in the development of pubic hair, body odor, skin oiliness, axillary hair, sexual ...

, and testosterone from the testicle in males during

puberty Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a ...

. The importance of human underarm hair is unclear. It may naturally wick

sweat Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...

or other moisture away from the skin, aiding ventilation. Colonization by odor-producing

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

is thereby transferred away from the skin (see

skin flora Skin flora, also called skin microbiota, refers to microbiota ( communities of microorganisms) that reside on the skin, typically human skin. Many of them are bacteria of which there are around 1,000 species upon human skin from nineteen phyla.P ...

). File:Armpit by David Shankbone.jpg , Male axilla File:Womans armpit.JPG , Female axilla

Function

Reducing friction

Armpit hair prevents skin-to-skin contact during activities that involve arm motion, such as running and walking. The same applies to pubic hair.

Spreading pheromones

The armpits release odor-containing pheromones, a naturally produced chemical that plays an important role in sexual attraction. Armpit hair traps odor, making the pheromones even stronger. A study in 2018 including 96 heterosexual couples found that there were stress-relieving benefits to smelling a romantic partner’s natural scent.

Impact of hair removal

Effect on odor

А 2012 study on the impact of hair removal on odor found that shaved armpits were rated the same as unshaved armpits.

Chemical absorption

A 2017 study on chemical absorption from deodorants as a result of hair removal showed an increase in chemical absorption from .01% to .06% where skin has been damaged by recent shaving. A 2003 study on aluminum antiperspirant usage and the age of breast cancer onset tentatively concluded that “underarm shaving with antiperspirant/deodorant use may play a role in breast cancer.”

References

External links

* {{DEFAULTSORT:Underarm Hair Upper limb anatomy Human hair