1 Alopecia areata is a hair-loss condition which usually affects the scalp. 2  Alopecia areata causes one or more patches of hair loss. 3  Alopecia areata affects both genders. 4  It is an autoimmune disorder, in which the immune system attacks hair follicles, is believed to cause alopecia areata.lopecia areata is occasionally associated with other autoimmune conditions such as thyroid disease, vitiligo, lupus, rheumatoid arthritis, and ulcerative colitis. The diagnosis or treatment of these diseases is unlikely to affect the course of alopecia areata.