What is Alopecia?
Alopecia areata causes development of bald patches on the scalp. Although it is a relatively uncommon cause of hair loss in children, about half of the people who do develop alopecia areata do so before their 20th birthday. A less common form of the disease, "alopecia totalis," results in loss of all the hair on the head.

Symptoms
Hair loss, usually in patchy, localized areas
Scalp in the areas of hair loss is smooth, without irritation, itching, or rash.
Sudden development of hair loss, without slow spreading of the affected area.
Hairs that do grow in the affected area are shaped like "exclamation points" (narrow at the base and wider at the tips).

Cause
The cause of alopecia areata is not known. It is thought to be an "autoimmune" disease. This means that the body confuses the hair follicle with an infecting or foreign object, and begins to attack it, much like it would fight an infection.

Risk Factor
People with family members with the disease are at a higher risk of developing alopecia areata, leading many to conclude there is an unidentified gene that makes certain people more likely to develop the disease.