Alopecia areata is a type of hair loss that occurs when the immune system mistakenly attacks hair follicle roots, where hair growth begins. It is most common in people younger than 20, but children and adults of any age may be affected.

• Usually clumps of hair fall out, resulting in totally smooth, round hairless patches. In some cases the hair may become thinner without distinct patches of baldness. This may happen several times.
• In rare cases, complete loss of scalp hair and body hair occurs.
• Hair may regrow completely, partially, or not at all. In most people with the condition, the hair regrows within a year.

Medical treatments for alopecia areata may include medications that are either put on the scalp or injected. Because hair often regrows, treatment may not be necessary.