This Publication Is Searchable The Merck Manual of Diagnosis and Therapy Section 10. Dermatologic Disorders Chapter 116. Alopecia may result from genetic factors, aging, or local or systemic disease. Male-pattern alopecia is extremely common. It is familial and requires the presence of androgens, but the cause is unknown.
Hair loss begins in the lateral frontal areas or over the vertex.
If onset is in the mid-teens, subsequent alopecia commonly is extensive. Female-pattern alopecia is common. Alopecia areata is characterized by sudden hair loss in circumscribed areas usually in persons who have no obvious skin disorder or systemic disease. Any hairy area may be involved, the scalp and beard most frequently. The prognosis is poor if alopecia is extensive or begins before adolescence, but alopecia confined to a few areas is often reversed in a few months even without treatment, although recurrences are common.