Alopecia areata is a medical condition that affects the hair follicles and usually causes hair to fall out in small, round patches. In the United States, it is estimated that alopecia areata has affected four million people. This condition affects both men and women of all ages and ethnic backgrounds, and it usually begins in childhood. While there is no cure for alopecia areata, doctors may prescribe medications that are approved for other diseases to help hair grow back. Ongoing research is being done to better understand alopecia areata and hopefully develop effective treatments for this condition.