Androgenic hair
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Body hair is a common colloquial term for the terminal hair on the human body developing during and after puberty in contrast to the head hair and the less visible vellus hair. A medical term for it is androgenic hair since its growth depends primarily on the level of androgens (male hormones) containing within the individual human organism. Due to a normally higher level of androgens men tend to have visibly more androgenic hair than women so that this type of hair can be seen as a sign for sexual dimorphism and therefore a secondary sex characteristic.
[edit] Development and growth
The appearance of androgenic hair is caused by the rising level of androgens due to puberty that causes a transformation process of vellus hair into terminal hair on several parts of the human body. The hair follicles respond to androgens, primarily testosterone and its derivatives. The rate of hair growth and the weight of the hairs increase. Different areas respond with different sensitivities. As testosterone levels increase, the sequence of appearance of androgenic hair reflects the gradations of androgen sensitivity. The pubic area is most sensitive, and heavier hair usually grows there first in response to androgens.
Areas on the human body that develop terminal hair growth due to rising androgens in both sexes, men and women, are the axillary hair and the pubic hair. In contrast to that, normally only men grow androgenic hair in other areas. There is a sexual dimorphism in the amount and distribution of androgenic hair, with males having more terminal hair (particularly facial hair, chest hair, abdominal hair and leg and arm hair) and females having more vellus hair, which is less visible. The genetic disposition determines the sex-dependent and individual rising of androgens and therefore the development of androgenic hair.
