Underarm hair

Underarm hair, also known as axillary hair or armpit hair, is human hair in the underarm area (axilla).

In some cultures, underarm hair removal through shaving or other means is common, particularly among women.

Underarm or axillary hair goes through four stages of development, as staged by the Wolfsdorf Axillary Hair Scale, driven by weak androgens produced by the adrenal in males and females during adrenarche, and testosterone from the testicle in males during puberty.

The Wolfsdorf Axillary Hair Staging system provides a standardized method for assessing pubertal progression and androgenic activity in pediatric populations. Similar to Tanner Staging for pubic hair, it classifies axillary hair growth into four stages:

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).

Armpit hair prevents skin-to-skin contact during activities that involve arm motion, such as running and walking. The same applies to pubic hair.^{[better source needed]}

The armpits release odor-containing pheromones, naturally produced chemicals that play 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.

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