Alopecia areata is an autoimmune disorder also known as "spot baldness" that can result in hair loss ranging from just one area to every hair on the entire body. If a medicine is causing your hair loss, your doctor may be able to prescribe a different medicine or you may find you really don't need the medicine at all. About 3 or 4 months after an illness or a major surgery, you can suddenly temporarily lose a large amount of hair; this hair loss is related to the stress of the illness.
Hair loss may occur as part of an underlying disease, such as lupus or diabetes. In the past it was believed that baldness was inherited from a person's maternal grandfather; while there's some basis for this belief, both parents contribute to their offspring's likelihood of hair loss. Tumors and skin growths can also induce localized baldness.