When mice are exposed to sunlight-like UV rays, adding certain chemicals that neutralize harmful free radicals to sunscreen helps stop skin tumors better—without making the sunscreen block more UV rays. This suggests that these free radicals are a big reason why UV light causes skin cancer.

When mice are exposed to sunlight-like UV rays, adding two special chemicals to sunscreen barely boosts its ability to block UV light—from SPF 5 to 5.5—but even though the sunscreen doesn’t get much stronger, the mice still get far less skin cancer. So something else must be protecting them.

When mice get too much sun, certain harmful molecules in their skin cause redness, weaken their immune response, and can lead to skin cancer. Blocking these molecules helps sunscreens work better than just blocking UV rays.

In mice, certain chemicals that block harmful oxygen molecules can stop sunburn-like immune suppression caused by UV light—but if you mix those chemicals with sunscreen, they stop working as well, probably because sunscreen gets in the way.

In mice, certain antioxidants reduce skin swelling after sun exposure, which means free radicals cause inflammation—but they don’t help sunblock stop immune suppression, so these two effects happen through different paths.

Sunlight can create harmful molecules in your skin, but your body naturally produces nitric oxide to balance them out—this balance keeps your skin healthy.