The exact cause of alopecia areata is not known. 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. Scientists suspect that a combination of genes may predispose some people to the disorder. In those who are genetically predisposed, some type of trigger — perhaps a virus or a psychological trauma — may bring on the disorder.
As with other autoimmune disorders, it is believed that a genetic predisposition to the disorder exists and that the disorder is triggered. Triggers may be environmental, dietary, or psychological.
In alopecia areata, immune system cells called white blood cells attack the rapidly growing cells in the hair follicles. The affected hair follicles become small and drastically slow down hair production. Fortunately, the stem cells that continuously supply the follicle with new cells do not seem to be targeted. So the follicle always has the potential to regrow hair.