gradual decrease of scalp hair density in adults with transformation of terminal to vellus hairs which become lost as a result of familial increase susceptibility of hair follicles to androgen secretion following puberty. Two areas of the scalp are commonly affected in men; when it occurs in females it is associated with other evidence of excessive androgen activity, such as hirsutism. See: female pattern alopecia, male pattern alopecia. Syn: alopecia hereditaria, common baldness, patterned alopecia.