Colloquially body hair, is the terminal hair that develops on the body during and after puberty.
It is differentiated from the head hair and less visible vellus.
The growth of androgenic hair is related to the level of androgens in the individual. Due to a normally higher level of androgen, men tend to have more androgenic hair than women.
From childhood onward, regardless of gender, 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 varies from person to person.
Androgenic hair is more commonly known as body hair. It does not include the hair on the head or other smaller hairs, known as vellus hairs, which are much finer and lighter in colour. In many cases, areas on the human body that contain vellus hair will begin to produce darker, thicker body hair. An example of this is the growth of an adolescent's beard on a once smooth chin.
Androgenic hair follows the same growth pattern as the hair that grows on the scalp, only the anagen phase is shorter, and the telogen phase is longer.
While the anagen phase for the hair on one's head lasts for years, the androgenic hair growing phase lasts a few short 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
Vellus hairs are short, fine, light colour, and barely noticed hairs, which develop on most of the human body from childhood, regardless of sex.
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 – the number of hair follicle per area of skin – varies from person to person. They are usually less than 2 mm (1/13inch) long and the follicle are not connected to sebaceous gland.
Vellus hair is most easily observed on women and children, as they have less terminal hair to obscure it than adult men do.
Vellus hair is differentiated from the more visible terminal or androgenic hair, which develops only during and after puberty, and usually to a greater extent on males than on females
The growth of vellus hair is of a different growth cycle than terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair.
During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body.
These parts will have different levels of sensitivity to androgens (testosterone).
The pubic area is particularly sensitive to such hormones, as are the armpits which will develop axillary hair.
Pubic and axillary hair will develop on both men and women, to the extent that such hair qualifies as secondary sex characteristics
Although males will develop terminal hair in more areas. This includes facial hair, chest hair, abdominal hair, leg and arm hair, and foot hair.
Human females on the other hand can be expected to retain more of the vellus hair
