system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why does sunlight darken skin but lighten the colour of other surfaces?
gpt
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.