Alopecia areata (AA) is a condition affecting humans, in which hair is lost from areas of the body, usually from the scalp. Because it causes bald spots on the scalp, especially in the first stages, it is sometimes called spot baldness. In 1%–2% of cases, the condition can spread to the entire scalp (Alopecia totalis) or to the entire epidermis (Alopecia universalis). Conditions resembling AA, and having a similar cause, occur also in other species.
The condition affects 0.1%–0.2% of humans, occurring in both males and females.
Alopecia areata occurs in people who are apparently healthy and have no skin disorder. Initial presentation most commonly occurs in the late teenage years, early childhood, or young adulthood, but can happen with people of all ages.