Why Does Hair Get Lighter in the Sun?
Hair gets lighter in the sun because the melanin in it is destroyed by overexposure to ultraviolet light, according to Aaron Shafer, a Stanford University geneticist. Hair does not replace melanin that is destroyed.
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Hair vs. Skin
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Unlike skin, which can replace melanin that sunlight destroys, hair is dead tissue that cannot do repair itself. The skin darkens upon sun exposure because it produces melanin to protect itself from sun damage. Hair lightens because it cannot produce more melanin.
UV Damage
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UV radiation causes damage by oxidation. Not only does it cause bleaching in hair, it destroys other proteins and compounds that keeps hair manageable, like thiols. The oxidation of thiols makes hair stick together and tangle, according to Shafer.
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Prevention/Solution
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Wearing a hat and avoiding too much sun can keep hair from bleaching, according to Shafer. Applying sunscreen to the skin is also recommended, of course.
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