Hair follicle is one of skin appentages and contains hair bulge where stem cells for maintenance of epidermis, hair follicle and sebaceous gland. Terminal hair consists of hair cortex, medulla and cuticle. Hair follicle has hair cycle, repeating tissue regeneration and regression. There are three phases such as anagen, catagen and telogen. In androgenetic alopecia (AGA), anagen is shortened, resulting in miniaturization of hair follicle. Then, hair shaft diameter is also smaller. As a new AGA drug, dutasteride is interesting because there are some cases showing better effect by dutasteride than finasterid.