Alopecia is a general term for hair loss.
Alopecia areata is a specific, common cause of hair loss that can occur at any age. It usually causes small, coin-sized, round patches of baldness on the scalp, although hair elsewhere such as the beard, eyebrows and eyelashes, body and limbs can be affected.
Occasionally it can involve the whole scalp (alopecia totalis) or even all the body and scalp (alopecia universalis). It is not possible to predict how much hair will be lost. Regrowth of hair in typical alopecia areata is usual over a period of months or, sometimes, years, but cannot be guaranteed. The hair sometimes regrows white at least in the first instance. Further hair loss is not uncommon. In alopecia totalis and alopecia universalis the likelihood of total regrowth is less.