Alopecia totalis (AT) is a condition characterized by the complete loss of hair on the scalp. It is an advanced form of alopecia areata a condition that causes round patches of hair loss. Although the exact cause of AT is unknown, it is thought to be an autoimmune condition in which the immune system mistakenly attacks the hair follicles. Roughly 20% of affected people have a family member with alopecia, suggesting that genetic factors may contribute to the development of AT.