Underarm hair, also known as axillary hair or armpit 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 ...

in the

underarm The axilla (: axillae or axillas; also known as the armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and ...

area (''axilla'').

Development

Underarm or axillary hair goes through four stages of development, as staged by the Wolfsdorf Axillary Hair Scale, driven by weak

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

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 (including humans), typically peaks at around 20 years of age, and is involved in the development of pubic hair, body odor, skin oiliness#Oily skin, skin oiline ...

, 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 female, the testicles i ...

. The Wolfsdorf Axillary Hair Staging system provides a standardized method for assessing pubertal progression and androgenic activity in pediatric populations. Similar to

Tanner Staging The Tanner scale (also known as the Tanner stages or sexual maturity rating (SMR)) is a scale of physical development as pre-pubescent children transition into adolescence, and then adulthood. The scale defines physical measurements of developm ...

for pubic hair, it classifies axillary hair growth into four stages: * Wolfsdorf Stage 1 – No axillary hair * Wolfsdorf Stage 2 – Sparse, soft hair * Wolfsdorf Stage 3 – Coarser hair with increased volume * Wolfsdorf Stage 4 – Full adult-like axillary hair The importance of human underarm hair is unclear. It may naturally wick

sweat Perspiration, also known as sweat, is the fluid secreted by sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and Apocrine sweat gland, apocrine glands. The eccrine sweat glands are distribu ...

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

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

is thereby transferred away from the skin (see

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

). File:Armpit by David Shankbone.jpg , Male axilla File:Womans armpit.JPG , Female axilla File:Armpit of a Teenager,in developement,Mar 2013.jpg , 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.

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." However, later studies have disputed this and found no significant increase in breast cancer among users.

References

External links

* {{DEFAULTSORT:Underarm Hair Axillas Human hair