Characteristics No, there are broadly two types of body hair:
- Vellus hair which is thin, slow growing and light colored. Before adolescence, most of the body in both males and females is covered by vellus hair. After adolescence, females generally continue to have vellus hair into terminal hair in typical areas of the body (male pattern). When excessive growth of terminal hair of male pattern occurs in women, it is called hirsutism.
- Terminal hair which is coarse, fast growing and dark colored. Eyebrows, eyelashes, scalp hair are examples of terminal hair. After adolescence, males show conversion of vellus hair into terminal hair in typical areas of the body (male pattern). When excessive growth of terminal hair of male pattern occurs in women, it is called hirsutism.
Normal Hair Growth Hair grows in a cyclical pattern. It erupts from the hair root (follicle) situated in a deep layer of skin. After a period of active growth, the hair root enters a resting phase. Once growth restarts, a new hair erupts and the old hair is pushed out. The life–span of each hair is approximately 9–12 months, whether vellus or terminal hair develops in a given area depends broadly upon two factors:
- Hormones (Secretions of ductless glands which are released in extremely minute quantities directly into the blood): A group of hormones called androgens promote the conversion of vellus hair rate of androgen production and the duration of exposure to androgens. Some hair follicles, such as those on the eyebrows, eyelashes and scalp do not require androgens to produce terminal hairs. As the blood level of androgens is several times higher in males (after adolescence) compared to females, males develop terminal hair in typical areas of the body. If the blood levels of androgens rise in females, they too can develop terminal hair in such areas or in short, develop hirsutism.
- Response of the hair roots to blood levels of androgens: If the response of hair roots to androgens is excessive in a female, she can develop hirsutism even though blood level of androgens is normal.