White hair in alopecia areata: Clinical forms and proposed physiopathological mechanisms.

Alopecia areata is a common form of non-scaring type of hair loss. It is believed to be a consequence of an immune-mediated stimulus, probably involving autoreactive T-cells against antigens present in the hair follicle. The exact antigen is still unknown; however, some authors have proposed that melanogenesis-associated molecules might trigger autoimmunity. Although transient white hair regrowth is a common and well-known situation in alopecia areata, there are other different types of white hair phenomena in this context; including permanent white hair regrowth, spearing of white hair in a patchy pattern or spearing in a diffuse form giving the appearance of the so-called "overnight graying phenomena" or Canitis subita. In this review we aim to describe the different clinical aspects of white hair in alopecia areata as well as the proposed pathophysiological mechanisms involved in this phenomena.