Alopecia areata is a disease that affects both children and adults. Its prevalence is 1-2% of the population. The condition is caused by a cellular immune response, resulting in production of multiple pro-inflammatory cytokines around the hair follicle. Genetic predisposition also plays an important role, as approximately 25% of affected patients come from families with a history of alopecia areata. Patients with this condition are more likely to suffer from other diseases caused by autoimmunity, such as autoimmune thyroiditis or vitiligo. Atopic dermatitis and the Down syndrome are other conditions that predispose to a higher incidence of alopecia areata.

The following kinds of baldness are distinguished: diffuse alopecia areata, alopecia nodularis, alopecia totalis, i.e. total loss of hair on the scalp, and alopecia universalic, i.e. total loss of hair on other body parts as well. A characteristic feature of spot baldness are exclamation point hairs, which often indicate activity of the disease.