Alopecia areata causes single or multiple round, bald patches on the scalp, which may be self-limiting and may respond to local corticosteroid treatment. This form of alopecia is thought to be autoimmune, with >40% of patients having antimicrosomal antibodies. Thyroid disease may coexist in this group; no androgen abnormality appears to be present.

The most common form of alopecia is male-pattern baldness, called “alopecia androgenica.” This process, which may be extremely gradual, occurs to some extent in virtually all men and many women, but in different patterns. In women, the frontal fringe remains intact130 (Fig. 101-20). The characteristic abnormality is a gradual transition from terminal to vellus hair (see Fig. 101-6). However, frankly male-pattern baldness may also occur in women. This pattern is associated with significant elevations in circulating androgens, such as are observed when ovarian tumors are present. Two different types of androgen-related hair loss are found in women. The first and most common type is not usually associated with an increase in androgen production. The second is associated with increased androgen production and may coexist with other virilizing features (see Fig. 101-20).