Because everyone has different skin, everyone in the world tans at a different rate. Some people get a dark tan in only a few hours, while others may never tan and only burn.
Melanin, the type of pigment that makes up hair and eye color, also affects skin color. People with less melanin have fairer skin that burns more quickly and does not tan easily. People with more melanin can get a dark tan in just a few hours, but people with less melanin may take days to tan or may never really tan at all. Everyone should wear sunscreen when spending time in the sun, since the sun's ultraviolet light can cause DNA mutations that can lead to cancer. People with pale skin should especially be careful in the sun, since they do not have the melanin needed to protect their skin from being burned.