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Alopecia areata (AA), also known as spot baldness, is an autoimmune disease in which hair is lost from some or all areas of the body, usually from the scalp due to the body's failure to recognize its own body cells and destroys its own tissue as if it were an invader.〔Zoe Diana Draelos (August 30, 2007), (Alopecia Areata ). MedicineNet.com. Retrieved on December 2, 2007〕 Often it causes bald spots on the scalp, especially in the first stages. In 1–2% of cases, the condition can spread to the entire scalp (alopecia totalis) or to the entire epidermis (alopecia universalis). Conditions resembling AA, and having a similar cause, occur also in other species. == Classification == Commonly, alopecia areata involves hair loss in one or more round spots on the scalp.〔〔Marks, James G; Miller, Jeffery (2006). ''Lookingbill and Marks' Principles of Dermatology'' (4th ed.). Elsevier Inc. ISBN 1-4160-3185-5.〕 * Hair may also be lost more diffusely over the whole scalp, in which case the condition is called diffuse alopecia areata.〔 * Alopecia areata monolocularis describes baldness in only one spot. It may occur anywhere on the head. * Alopecia areata multilocularis refers to multiple areas of hair loss. * Ophiasis refers to hair loss in the shape of a wave at the circumference of the head. * The disease may be limited only to the beard, in which case it is called alopecia areata barbae.〔 * If the patient loses all the hair on the scalp, the disease is then called alopecia totalis. * If all body hair, including pubic hair, is lost, the diagnosis then becomes alopecia universalis.〔(Skin Conditions: Alopecia Areata ). WebMD. Retrieved on December 2, 2007.〕 Alopecia areata totalis and universalis are rare.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Alopecia areata」の詳細全文を読む スポンサード リンク
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