Alopecia areata is a hair loss disorder that is mediated by the immune system. Both males and females of all ages and ethnicities may develop alopecia areata. Any hair-bearing region of the body can be affected. The most common clinical presentations are called alopecia areata, alopecia totalis, and alopecia universalis. The term alopecia areata is used when there are round to oval patches of hair loss present. Alopecia totalis refers to loss of all scalp hair and alopecia universalis to loss of all scalp and body hair.
The hair loss that occurs in alopecia areata may appear suddenly with no symptoms or there may be mild itching or tingling. Hair fibers usually fall out by their “roots,” an event that occurs with normal daily hair loss but in alopecia areata, the numbers of fibers in the loss phase are significantly increased especially in the involved areas. After shedding occurs, regrowth usually does not proceed quickly and the involved areas may remain bald for some time. This is not because the hair follicle has been destroyed but rather either an “arrest” of hair growth or a prolongation of the resting phase in the hair cycle occurs.