Alopecia areata is a type of patchy hair loss that occurs when your immune system mistakenly attacks hair follicles, which is where hair growth begins. The damage to the follicle is usually not permanent. Experts do not know why the immune system attacks the follicles. Alopecia areata is most common in people younger than 20, but children and adults of any age may be affected. Women and men are affected equally.
Alopecia areata usually begins when clumps of hair fall out, resulting in totally smooth, round, shiny hairless patches on the scalp or body. In some cases the hair may become thinner without noticeable patches of baldness, or it may grow and break off, leaving short stubs (called “exclamation point” hair). In rare cases, complete loss of scalp hair and body hair occurs. The hair loss often comes and goes, hair will grow back over several months in one area but will fall out in another area.