Abstract
Alopecia areata (AA) is an autoimmune disorder in which immune attack of the anagen follicle causes hair loss in approximately 2% of the population. Although the pathogenesis of AA has not been fully determined, most likely it is mediated by a variety of factors including cellular/humoral immunity and genetic predisposition. Researchers have been interested in the possible role of the complement pathway in AA since the 1970s. Given recent evidence suggesting that complement plays a role in many immunologic and inflammatory dermatologic diseases including systemic lupus erythematosus, bullous diseases, angioedema, lipodystrophy, and skin infections, it is likely that complement also contributes to AA pathogenesis. Although early serum studies and immunohistochemical staining have been unimpressive, recent genetics studies may provide evidence that complement does indeed contribute to AA. By determining if complement plays a role in AA, options for novel targeted treatments will become available for those patients with refractory disease.