Sunscreens are chemicals that are designed to be absorbed by the skin in order to form a sun barrier so you do not get first-degree or even second-degree burns (blisters). Many of the chemicals have been broken down into tiny particles so that they can be sprayed or absorbed more easily. There is clear evidence that they prevent sunburn, but there is very little known about the safety of these chemicals and their effectiveness in reducing skin cancer from sun exposure. There are also studies whose statistical evidence shows that in some cases these chemicals may actually increase your risk of cancer. There are three primary concerns with the chemicals in sunscreen:
1) They are free-radical generators which breakdown the DNA in cells and potentially make them more prone to cancer.
2) They often have strong estrogenic effects, meaning the chemicals could actually interfere with normal sexual development.