There are several different hypotheses as to what causes alopecia areata. Genetic factors seem to play an important role since there is a higher frequency of a family history of alopecia areata in people who are affected. Alopecia areata appears to also have an autoimmune factor causing the patient to develop antibodies to different hair follicle structures. Certain chemicals that are a part of the immune system called cytokines may play a role in alopecia areata by inhibiting hair follicle growth. Some studies show that emotional stress may also cause alopecia areata.
Hair loss occurs because the hair follicles in a discreet area all enter the telogen or late catagen stage of hair growth. In the catagen stage the hair follicle stops growing and in the telogen stage it falls out. Normally hairs are going through these stages at random and the growing hairs on the rest of the head outnumber the hairs that fall out. In alopecia areata, something causes all the hairs in a certain area to enter the telogen or catagen stage at the same time.