白毛症

Also known as poliosis circumscripta, white forelock, Mallen streak

Poliosis circumscripta, commonly referred to as a "white forelock", is a condition characterized by localized patches of white hair due to a reduction or absence of melanin in hair follicles. Although traditionally associated with the scalp, poliosis can affect any hairy area on the body, including eyebrows, eyelashes, and beards. Microscopically, poliosis is marked by the lack of melanin or melanocytes in the hair bulbs, though epidermal melanocytes typically remain unaffected unless associated with conditions like vitiligo.