Alopecia areata is a prevalent autoimmune skin disease resulting in the loss of hair on the scalp and elsewhere on the body.It usually starts with one or more small, round, smooth patches on the scalp and can progress to total scalp hair loss (alopecia totalis) or complete body hair loss (alopecia universalis).lopecia areata is a prevalent autoimmune skin disease resulting in the loss of hair on the scalp and elsewhere on the body.