Melanin
We could see that we are all having different skin, eye colors. did you ever think that how is it changing for each and everyone?
There is a coloring pigment in our body, which is located under our outer skin. This pigment is produced by melanocyte cells. Skin and eye colors will be changes with respect to amount of melanin we have. Black & brown skin peoples have more melanin than light skin peoples have.
Use of melonin:
Melonin protects us from skin damage, and UV ray radiation effect from the sun and even light-skinned peoples also responds to these by producing more melanin and it creates the "tanning".
Demerits of more melanin:
Pimples, rashes, scratches could stimulate production of excess melanin which creates dark marks, patches in our skin.