Alopecia is the medical term for baldness; there are various types of alopecia, including alopecia areata, a condition that causes a person’s hair to fall out. It is an autoimmune disease; that is, the person’s immune system attacks their body, in this case, their hair follicles. When this happens, the person’s hair begins to fall out, often in clumps the size and shape of a quarter. The extent of the hair loss varies; in some cases, it is only in a few spots. In others, the hair loss can be greater.