Alopecia areata (AA) is a common condition affecting humans, in which hair is lost from some or most areas of the body, usually from the scalp. It causes bald spots on the scalp, especially in the first stages, for that reason, it is sometimes called spot baldness. In the 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.