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Asked by to Kieren, Rowena, Roy on 20 Mar 2014. This question was also asked by .
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Roy Adkin answered on 20 Mar 2014:
UV radiation in the suns electromagnetic emissions burns the skin. this produces a pigment called melanin which causes the skin to darken as this helps protect the skin against the full force of the energy (although it is still very strong and you should stay covered up or slap on lots of sunscreen). Your hair lightens because the sun bleaches the colour by breaking down the melanin. The hair is dead and so stays lighter as there is no melanin being produced to replace that destroyed (except from the root as it grows) but as your skin is alive it replaces and increases production of melanin which is why it darkens but doesn’t lighten.
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Rowena Fletcher-Wood answered on 20 Mar 2014:
According to this article (https://news.brown.edu/pressreleases/2011/11/melanin) your skin doesn’t produce more melanin after it has been destroyed (otherwise we would bleach first, surely? whilst some people tan without even going red under UV radiation!) – no, your skin… HAS EYES. That is, it has a UV photosensors which detect the incoming light and respond by excreting more melanin to protect you before you get burnt. It can obviously be too slow if the sun is powerful enough and you get burnt anyway, but if you are already darker you have a head start which is why dark skin is common in hot climates. Your hair does not have eyes.
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