For decades, irresponsible cosmetic companies and a small group of very vocal, publicity-seeking dermatologists have strongly advocated that chemical sunscreens should be heavily applied before any exposure to sunlight, even on young children. They insisted that such sunscreen use would prevent skin cancer and protect your health. This was despite of a lack of any adequate safety testing of these chemicals. (It should be emphasized that most dermatologists are much more cautious and careful.)
On the other hand, over the past decade, many scientists studying cancer have come to virtually the opposite conclusion; that is, the use of sunscreen chemicals may be increasing the incidence of cancer and that sunlight exposure may actually decrease human cancer rates and improve your health.
It now appears that many heavily-used chemical sunscreens may actually increase cancers by virtue of their free radical generating properties. And more insidiously, many commonly used sunscreen chemicals have strong estrogenic actions that may cause serious problems in sexual development and adult sexual function, and may further increase cancer risks.
It is not that these compounds were ever viewed as benign substances. Organic chemists have been long aware of the dangers of compounds in chemical sunscreens. Such chemicals are widely used to start free radical reactions during chemical synthesis. These chemicals are the dangerous types that one carefully keeps away from your skin while working in a laboratory. To use them, you mix them into a combination of other chemicals, then flash the mixture with an ultraviolet light. The ultraviolet absorbing chemicals then generate copious amounts of free radicals that initiated the desired chemical reactions.
Despite the medical establishment's near unanimity on the issue of sunlight exposure, on other health issues in the past, serious errors been promoted to the public.