Sunscreen Could Be Giving You Skin Cancer

The research, carried out at Missouri University of Science and Technology, looked into what happens to the compounds in sunscreen when they're exposed to light. In particular, they found that zinc oxide—a staple ingredient in sunscreen—undergoes a chemical reaction when it's illuminated by bright light that may release unstable molecules known as free radicals.

Those free radicals readily bond with other molecules, but in the process they can damage cells or the DNA contained within those cells, in turn increasing the risk of skin cancer. The tests, which were carried out in the lab using lung cells covered in zinc oxide solution, suggest that it is UV light which causes the reaction to take place most strongly. Which is, you know, precisely the kind you use sunscreen to protect yourself from.
The research, which is to be published in the Journal of Toxicology and Applied Pharmacology, suggests that the harmful effects of the free radicals increases the longer zinc oxide is exposed to sunlight. After 3 hours of UV exposure, half of the lung cells covered in zinc oxide solution died. After 12 hours, that increased to 90 percent.