Why does sunlight darken skin but lighten the colour of other surfaces?
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Sunlight can breakdown the molecules that give things their coloring, lightening them. This works for objects because they are not alive, and so can’t replace the destroyed color molecules.
You, however, are alive. Your body will actively choose to produce more skin pigment molecules if you get exposed to a lot of sunlight. It does this because the pigment protects you from the damage sunlight can do to you.
The tanning of skin is much more complicated than photo-bleaching of pigments. It’s a biological process that manufactures new pigments in response to damage from the Sun’s UV light, in order to prevent future sunburns. In photo-bleaching, the pigments that give a substance color are damaged by UV light, changing their chemical properties and destroying their color, and that’s it.
The tanning bit is more like our bodies going “oh no… radiation. Protect everything with these dark pigments (which absorb light)”
Inanimate objects can’t really make or redistribute more pigments.
AI Elon:
Sunlight darkens skin because it contains UV radiation that triggers a reaction in our body to create a dark pigment called melanin. The pigment helps protect our skin from DNA damage, which can cause skin cancer. Other surfaces, on the other hand, do not have this reaction and only get lighter when exposed to sunlight. This is because the UV radiation in sunlight bleaches the color out of those surfaces. So while the UV light darkens our skin, it lightens our hair and clothes.
Your body creates a protective layer in response to UV radiation damage. This layer is made from melanin, and it is darker-colored.
The same radiation damage that gives you a sunburn will also damage inanimate objects, too. They are not alive and cannot try to protect themselves, so some molecules within that object simply get destroyed. This often includes the molecules that make something have a color.
Besides what these other fine people have mentioned, We aren’t the only things that get darker with sunlight. I do some wood working and a lot of wood gets darker when laying in the sun for a while
Our skin darkens to protect from the sun, while nonliving things lighten because the molecules that give color break down
Wood also darkens in the sun but continued exposure will bleach it as well, turning the wood gray
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