androgenetic alopecia, a common progressive, diffuse, symmetric loss of scalp hair. In men it begins in the 20s or early 30s with hair loss from the crown and the frontal and temple regions, ultimately leaving only a sparse peripheral rim of scalp hair (male pattern alopecia, often called male pattern baldness). In females it begins later, with less severe hair loss in the frontal area of the scalp. In affected areas, the follicles produce finer and lighter terminal hairs until terminal hair production ceases, with lengthening of the anagen phase and shortening of telogen of the hair cycle. The cause is unknown but is believed to be a combination of genetic factors and increased response of hair follicles to androgens. Additional medical conditions may be involved with hair loss. See also male pattern alopecia.
