A recent study involving more than 700 sunscreens found that 84% are not cutting it. Many fail to provide adequate protection from harmful rays, or break down too quickly in the sun, msnbc.com reports. What's more, consumers often rely on SPF numbers to choose a product. But SPF measures UVB rays, which cause sunburn, not UVA rays, which can lead to skin cancer.
Some 8,000 Americans die each year of melanoma, a form of skin cancer. But at the moment, there is no standard way to measure UVA protection; and labels like "broadspectrum," are often misleading. The FDA is promising a new regulation shortly. For now, dermatologists advise following standard safety tips--e.g., apply sunscreen early and often, and wear a hat. (Read more sunscreen stories.)