Question: Why does the sun lighten our hair but darken our skin?

Jon Copley answered on 16 Jun 2010:

Our skin darkens in sunlight because special cells in the skin react to the light and make a substance called melanin. It’s this melanin that darkens our skin, because it gets carried to skin cells, where it sits on top of their nucleii like an umbrella sun-shade, to protect them (intense sunlight can damage the DNA in the nucleii of cells, causing mutations and even skin cancer).

But hair is different because once a hair has grown out of the follicle that carries its roots, it is beyond the reach of the cells that make melanin. Melanin breaks down in sunlight, so once sunlight breaks down the melanin that was put into the hair as it grew out of the follicle, that melanin can’t be replaced. And when the melanin in hair breaks down without being replaced, the hair gets lighter in colour.

So there’s the answer – our skin gets darker because more melanin is added to it, while our hair gets lighter because the melanin in it gets broken down and can’t be replaced.