Why the Sun Lightens Our Hair
A: This is an interesting question and to answer it, you should think about the nature of skin, versus the nature of hair. The two have many similarities, but are different in some key ways. Specifically, skin is comprised of layers of cells of living tissue, while the hair is made of keratinized (hardened) protein and is dead tissue.
Usually, those with more melanin are less affected by the sun's rays (at least in that they are less likely to get sunburn). And the fact that the melanocytes in the skin produce additional melanin when exposed to the sun's rays is why some people grow tan from being in the sunshine.
When the hair is exposed to the sun, the sun's radiation breaks up the pigment molecules in the hair which results in a lightening of the color (or in some cases a fading of more vibrant artificial colors). The hair lacks the means to protect itself from sun damage naturally, which is why there are products made for use in the sun to protect the hair.
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See also:
Hair and sun exposure
Sun block for hair
Does the sun make your hair grow faster?
Does the tanning bed hurt your hair in any way?
