poliosis

Poliosis is a localized patch of white or gray hair caused by a loss or absence of pigment-producing melanocytes in the hair follicle. The affected area can occur on the scalp, eyebrows, eyelashes, or beard and may be present at birth or develop later in life. The condition is typically permanent for the patched hair, though surrounding hair may remain normally pigmented.

Causes and associations include genetic conditions such as Waardenburg syndrome, which often features poliosis together with dystopia canthorum, and piebaldism, where a white forelock is common. Poliosis can also accompany autoimmune or inflammatory pigmentary disorders, notably vitiligo and Vogt-Koyanagi-Harada disease, in which melanocyte loss can extend to hair follicles. Acquired poliosis may follow inflammatory scalp conditions, infections, trauma, or systemic illness. In some cases, the cause remains unknown.

Pathophysiology involves disruption or loss of melanocytes in the hair follicle, leading to reduced or absent melanin in the hair shaft. The patch is typically circumscribed and may remain stable or change slowly over time. Poliosis may occur with or without accompanying skin depigmentation; in vitiligo, for example, poliosis can precede visible skin changes.

Diagnosis is usually clinical, based on appearance and history. Dermoscopy or biopsy is rarely required but may be used to distinguish poliosis from other causes of white hair. Differential diagnoses include leucotrichia from vitiligo, generalized albinism, or other pigmentary disorders.

Management focuses on addressing any underlying condition, when identified. There is no specific treatment to restore pigment in the affected hairs; cosmetic options can conceal the patch, and prognosis depends on the associated disease and its course.