Why does the sun lighten our hair, but darken our skin?

1. 60

   ChilliWillyposted 13 years ago

   Why does the sun lighten our hair, but darken our skin?

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2. 73

   lone77starposted 13 years ago

   ChilliWilly, nice question. I'm sure there is a deep answer to be found through Google, but right off the top of my head, the first has to do with photo-chemistry and the second has to do with photo-biology.
   
   The pigment in hair is broken down by high-energy light waves. In the upper atmosphere, gas molecules are photo-dissociated (split apart by those energetic photons). That's how we get ozone in the upper atmosphere; after that photo-dissociation, the lonely, but charged oxygen atoms decide to make a threesome. In hair, the chemical which acts as a pigment absorbs one set of frequencies. The reduction of that chemical by photo-dissociation means there is less of that chemical to absorb those frequencies. That's photo-chemistry.
   
   The skin, when it detects ultraviolet, sends out melanin to protect it from those harsh rays. Melanin is a darker color. This is photo-biology.
   
   That's my educated guess.

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3. 53

   Jack4952posted 13 years ago

   Hair (above the scalp) is composed primarily of dead protein. The UV light from the sun denatures (breaks apart) this protein and creates tiny air spaces within the hair shaft. These air spaces refract light, so the hair appears lighter in color. When the air spaces get LARGER, the hair appears gray.
   
   The skin (epidermis) is live tissue - except for the outer-most layer of dead epithelial cells. The live epithelial cells contain MELATONIN, which appears dark. When these cells are exposed to UV light, the cell (as a protective measure) synthesizes additional melatonin. The more melatonin in these skin cells, the darker one's skin appears.
   
   It's that simple!
   
   (I am a medical doctor, but this is very basic stuff.)

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