الفهرس 
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Abstract
Alopecia areata is a chronic inflammatory disease that involves the HF. This inflammation is caused by a T-cell mediated autoimmune mechanisms occurring in genetically predisposed individuals. Environmental and psychological triggers may be involved in its aetiology.In AA, hair shedding occurs even before the anagen starts leaving the HF empty (kenogen). Thus, AA is generally a disorder of hair cycling and is considered to be a state of kenogen Many etiologic factors have been suggested to contribute to the development of AA. These include stress, infectious agents, vaccinations, hormonal factors, and genetics. The exact cause is still unknown. Most of the recent literature supports autoimmunity as the major pathogenic process in AA Alopecia areata only occurs when the physiological IP of the HF is lost. It has been shown that locally generated immunosuppressive agents, such as TGF-β1 and 2, alpha-melanocyte-stimulating hormone (α-MSH), calcitonin gene-related peptide and vasoactive intestinal peptide all serve as important guardians of HF IP as they inhibit accumulation and/or activation of autoreactive lymphocytes and are capable of down-regulating excessive, ectopic expression of HF autoantigen presenting MHC class I and class II molecules.