Alopecia areata is an acquired skin disease that can affect all hair-bearing skin and is characterized by localized areas of non-scarring hair loss. Alopecia areata is occasionally associated with any other external or internal medical problems. Most often these bald areas regrow their hair spontaneously. Alopecia areata is rare before the age of 3 years. There seems to be a significant to inherit the tendency to develop alopecia areata from ancestors.
Alopecia areata is caused by an abnormality in the immune system. As a result, the immune system attacks particular tissues of the body. In alopecia areata, for unknown reasons, the body's own immune system attacks the hair follicles and disrupts normal hair formation. Biopsies of affected skin show immune lymphocytes penetrating into the hair bulb of the hair follicles.
Alopecia areata tends to occur most often in adults 30 to 60 years of age. However, it can also affect older individuals and, rarely, young children. Alopecia areata is not contagious. It should be distinguished from hair shedding that may occur following the discontinuation of hormonal estrogen and progesterone therapies for birth control or the hair shedding associated with the end of pregnancy.