Alopecia areata is an autoimmune disease. Normally the immune system protects the body against infection and disease. In an autoimmune disease, the body’s immune system mistakenly attacks some part of your own body. In alopecia areata, the immune system attacks the hair follicles.

The cause is not known. Scientists think that a person’s genes may play a role. For people whose genes put them at risk for the disease, some type of trigger starts the attack on the hair follicles. The triggers may be a virus or something in the person’s environment.