Alopecia areata (AA) causes hair loss in small, round patches that may go away on their own, or may last for many years. Nearly 2% of the U.S. population (about four million people) will develop AA in their lifetime. Some people with AA (about 5%) may lose all scalp hair (alopecia totalis) or all scalp and body hair (alopecia universalis). The immune system, for unknown reasons, attacks the hair root and causes hair loss.

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