Basic information description Sudden hair loss in circular patches on the scalp. The hair loss does not occur with other visible evidence of scalp disease. It can involve hair on the scalp, eyebrows, eyelashes, genital area, or underarms (sometimes). Alopecia can occur at any age, from birth to older adults. Many cases start before age 20. frequent signs and symptoms Sudden hair loss in sharply defined circular patches. In rare cases, body hair loss may be total (alopecia universalis). ...