Biology of Hair Growth
In this chapter, structural and biologic characteristics of hair follicles in different body regions are reviewed and regulatory factors influencing both normal and abnormal hair growth are discussed, with emphasis on androgenic action associated with both hirsutism and androgensic alopecia.
Abstract
Hair growth in the human body generally shows a distinctive regional pattern and sexual dimorphism, although there are some noticeable differences among different races and kinships. Thus, hair growth in different body regions is genetically predetermined. However, the development of normal masculine and feminine patterns of hair growth is apparently dependent on normal levels of sex steroids, particularly androgens in both men and women. Prepubertal castrates lack the secondary sex hair growth as well as the masculine type of hair growth in the face and other body regions. Women with excess androgen production due to adrenal and ovarian disorders show a masculine type of hair growth in the face (hirsutism) as well as frontal alopecia. Both the development and abnormal changes of hair growth are fundamentally a result of transformation of hair follicles, either enlargement or diminution of follicular size. In this chapter, I will review structural and biologic characteristics of hair follicles in different body regions and discuss regulatory factors influencing both normal and abnormal hair growth, with emphasis on androgenic action associated with both hirsutism and androgenic alopecia.