I, like so many other people, get fairly burnt during the summer. In Caucasians, melanin production is stimulated by ultraviolet light. This is the tanning process, and it takes time. Short exposure over the course of a week is usually the way to go to get a safe tan. The pigment produced can absorb some of the UV light and prevent more severe damage.
With exposure to UVB (280-315 nm) light, the burning process can take place within fifteen minutes. It’s usually somewhat later that the effect start to show. The skin becomes pink or red as blood flow increases in the capillaries at the burnt skin. (this is why you can press on the skin and it will turn lighter, the blood is forced out, the blood refills the capillaries and the redness returns) The blood carries nutrients to repair or replace the damaged skin. This is an inflammatory process caused by prostoglandins which are associated with pain. Among the damage done to the body by ultraviolet light is the formation of pyrimidine dimers. Neighboring pyrimidines in DNA or RNA bind to each other leading to perpetuated mutations if not properly repaired. The most common way for the body to deal with the kinks from this DNA damage is for enzymes to cut the section out. This damage could potentially lead to cancer as the mutations pile on top of one another.
Lately I’ve heard mention of sunscreen causing cancer, not sun exposure. I’ve done a fair bit of research and haven’t found any actual studies to support this thought. There are plenty of studies showing links between cancer and UV exposure. Even with the increasingly popular (because they go on clear) nanoparticle sunscreens, all available studies seem to show that they are safe.