Alopecia areata is a prevalent autoimmune skin disease resulting in the loss of hair on the scalp and elsewhere on the body. It usually starts with one or more small, round, smooth patches on the scalp and can progress to total scalp hair loss or complete body hair loss. The scalp is the most commonly affected area, but the beard or any hair-bearing site can be affected alone or together with the scalp.
In men, initial signs are seen in teenage years, half of men are affected by the age of 50, rate of progression and severity of end result are extremely variable. In women, reported prevalence rates vary widely, it affects around one third of white Caucasian women over the age of 70. There is ethnic variation with it being less common in women of Oriental origin. Rate of progression is variable but women rarely go completely bald.