Poliosis is the decrease or absence of melanin (or color) in head hair, eyebrows, or eyelashes. It can give rise to a "Mallen Streak" that can be hereditary.
Catherine Cookson

Catherine Cookson

Dame Catherine Cookson DBE was a British author. She became the United Kingdom's most widely read novelist, with sales topping 100 million, while retaining a relatively low profile in the world of celebrity writers...

 wrote a novel and later a TV series called The Mallen Streak, where a family had the condition. Sports presenter Dickie Davies

Dickie Davies

Richard "Dickie" Davies is a British television presenter, best known for presenting World of Sport from 1968 until 1985....

 was famous for this feature. People with Waardenburg syndrome

Waardenburg syndrome

Waardenburg syndrome Waardenburg syndrome Waardenburg syndrome (also Waardenburg­ Shah Syndrome, Waardenburg-Klein syndrome, Mende's syndrome II, Van der Hoeve-Halbertsma-Waardenburg syndrome, Ptosis-Epicanthus syndrome, Van der Hoeve-Halbertsma-Gualdi syndrome, Waardenburg type Pierpont,[5] Van...

 usually present this symptom, as do 60% of patients with tuberous sclerosis

Tuberous sclerosis

Tuberous sclerosis or tuberous sclerosis complex is a rare multi-system genetic disease that causes non-malignant tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. A combination of symptoms may include seizures, developmental delay, behavioral...

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