Poliosis is the decrease or absence of melanin (or colour) in head hair, eyebrows, or eyelashes. It can give rise to a "Mallen Streak" that can be hereditary. Catherine Cookson wrote a novel and later a TV series called The Mallen Streak, where a family had the condition. Sports presenter Dickie Davies was famous for this feature. People with Waardenburg syndrome usually present this symptom.

This condition can cause white patches (singular or multiple - usually single) on the hair. Most people confuse these white patches as simple birth marks.

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