I'm not the super scientific person that much, but, some people have more melanin in their skin. that is what makes a person darker, or lighter.
Example: my skin tone is called gold, even though its not.
It's very interesting, because if the sun wasn't their, we would all be as light as the purest snow.
My oldest brother usually says, that it is good that God put the sun where it is today!
I'm glad I could kind of give you an example of too much sun... kind of...
but, some people have different genes that can be used to make your skin kind of immune to sun-rays.
I know a person kind of like that. His Dad is Jamaican, and his mom is, I think Spanish or something. He has skin kind of like mine, but he has never gotten a sun burn in his life.
Or some people put sun screen/sun block to help them not get a sun burn.
That is one way @Missy_Vonheart!