Axillary hairs
Hirci
Definition
Axillary hair refers to the terminal hair that grows in the axillary (underarm) region, typically appearing during puberty as a secondary sexual characteristic. Its development is primarily driven by adrenal and gonadal androgens, particularly dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), and testosterone.
Key Features
Onset: Axillary hair development generally begins during adrenarche and puberty, typically between ages 10–14 in both sexes. In the Tanner staging system, axillary hair appearance corresponds to Tanner stage 4 of pubic hair development in most individuals.
Type: Axillary hair is classified as terminal hair — coarse, pigmented, and medullated — as opposed to the fine vellus hair that covers most of the body before puberty.
Hormonal regulation: Its growth is androgen-dependent. The conversion of vellus follicles to terminal follicles in the axilla is mediated by the action of 5-alpha reductase and androgen receptors within the hair follicle.
Function: While the precise biological function is debated, proposed roles include:
Reduction of friction between the arm and torso during movement.
Facilitation of pheromone dispersal from apocrine sweat glands concentrated in the axilla.
Wicking of moisture away from the skin surface.
References
