RESUMO
The scalp hair is composed of one hundred thousand of hairs. Each hair goes through the three phases of the hair cycle, which causes the hair to turn from an anagen hair into a catagen hair, then into a telogen hair, and finally into a new anagen hair. The number of hairs is maintained at a relatively constant level because each hair has its own hair cycle. The hair of Koreans is relatively thicker than that of Caucasians and Africans but its growth rate and density are lower. There are various factors that influence hair growth such as hormones, nutritional status, and drugs. However, androgen is most important among these factors and, particularly, androgenetic alopecia is caused by androgen and genetic factors. Because excessive dihydrotestosterone produced by 5alpha-reductase is of the greatest importance in androgenetic alopecia, finasteride or dutasteride, which inhibits the action of 5alpha-reductase, is effective in treating androgenetic alopecia. Also, minoxidil is widely used as it promotes hair growth. Furthermore, there are various types of hair diseases and specialized examination is required for differential diagnosis.