Pilosity

Body hair
Hair on the arm.
Example distribution of body hair in females and males.
Anatomical terminology []

Body hair, or androgenic hair, is the terminal hair that develops on the human body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which are much finer and lighter in color. The growth of androgenic hair is related to the level of androgens (often referred to as male hormones; due to the production levels in males being higher on average, but it is actually present in both sexes, and therefore is a unisex hormone) in the individual.

From childhood onward, regardless of sex, vellus hair covers almost the entire area of the human body. Exceptions include the lips; the backs of the ears; the palms of hands; the soles of the feet; certain external genital areas; the navel; and scar tissue. The density of hair – i.e. the number of hair follicles per unit area of skin – varies from person to person. In many cases, areas on the human body that contain vellus hair will begin to produce darker and thicker body hair, such as the first growth of beard hair on a male and female adolescent's previously smooth chin; although it may appear thinner on the female. Some men don't have chest hair.

Androgenic hair follows the same growth pattern as the hair that grows on the scalp, but with a shorter anagen phase and longer telogen phase. While the anagen phase for the hair on one's head lasts for years, the androgenic hair growing phase lasts a few months. The telogen phase for body hair lasts close to a year. This shortened growing period and extended dormant period explains why the hair on the head tends to be much longer than other hair found on the body. Differences in length seen in comparing the hair on the back of the hand and pubic hair, for example, can be explained by varied growth cycles in those two regions. The same goes for differences in body hair length seen in different people, especially when comparing men and women.