Alopecia areata is a condition that causes hair to fall out in small patches, which can be unnoticeable. These patches may connect, however, and then become noticeable. The condition develops when the immune system attacks the hair follicles, resulting in hair loss.
Sudden hair loss may occur on the scalp, and in some cases the eyebrows, eyelashes, and face, as well as other parts of the body. It can also develop slowly and recur after years between instances.
The condition can result in total hair loss, called alopecia universalis, and it can prevent hair from growing back. When hair does grow back, it’s possible for the hair to fall out again. The extent of hair loss and regrowth varies from person to person.