Underarm hair, also known as axillary hair or armpit hair, is the
hair in the
underarm area (axilla).
Development
Underarm or axillary hair goes through four stages of development, driven by weak
androgens produced by the adrenal in males and females during
adrenarche, and testosterone from the testicle in males during
puberty.[2]
The importance of human underarm hair is unclear. It may naturally wick
sweat or other moisture away from the skin, aiding ventilation. Colonization by odor-producing
bacteria is thereby transferred away from the skin (see
skin flora).[3]
Male axilla
Female axilla
Axillia of a pubescent male, note the short, stray hairs characteristic of this stage (Wolfsdorf 2)
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.[4][better source needed]
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.[5]
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.[6]
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.[7]
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.”[8]
^Hofer MK, Collins HK, Whillans AV, Chen FS (January 2018). "Olfactory cues from romantic partners and strangers influence women's responses to stress". Journal of Personality and Social Psychology. 114 (1): 1–9.
doi:
10.1037/pspa0000110.
PMID29293018.
S2CID40410769.
^Kohoutová D, Rubešová A, Havlíček J (April 2012). "Shaving of axillary hair has only a transient effect on perceived body odor pleasantness". Behavioral Ecology and Sociobiology. 66 (4): 569–581.
doi:
10.1007/s00265-011-1305-0.
ISSN0340-5443.
S2CID16607684.
^McGrath KG (December 2003). "An earlier age of breast cancer diagnosis related to more frequent use of antiperspirants/deodorants and underarm shaving". European Journal of Cancer Prevention. 12 (6): 479–485.
doi:
10.1097/00008469-200312000-00006.
PMID14639125.
S2CID24938503.