Using sunscreen every day, year round, not only staves off skin cancer, it also keeps UV rays from causing wrinkles, brown spots, and prematurely aged skin. Dermatologists have long thought that daily sunscreen usage slows skin aging, but past studies have been on mice, not humans. Now we have full proof. In a study, Australians who wore SPF 15 or higher every day had no detectable increase in skin aging after 4.5 years. Lead researcher Adele Green says she's sure UV rays – not natural aging – caused most, if not all, of the changes in the occasional sunscreen users' skin, since all participants were under age 55. "Skin aging due to sun damage is cumulative," says Green. "Daily sunscreen use can slow aging, as long as your skin is not already showing very severe changes."