Alopecia areata is hair loss of unknown cause, characterized by round patches of complete baldness.
The specific cause of alopecia areata is unknown. A family history of alopecia is present in about a fifth of all cases. Alopecia areata is occasionally associated with autoimmune diseases.
Alopecia may also occur as alopecia totalis with complete loss of scalp hair or as alopecia universalis with total loss of all body hair.