What causes alopecia areata?

In alopecia areata, patches of hair loss appear suddenly.  The hair loss is often discovered by a barber or hairdresser.

The hair-growing tissue stops making hair, and the hair then falls out from the roots.  Why this happens is a mystery.  Alopecia areata is not contagious, not caused by foods, and not the result of nervousness. It sometimes runs in families.