![]() That’s why you need to look for a broad-spectrum sunscreen, which protects against both UVA and UVB. to 4 p.m., UVA rays are present as long as there is daylight. Unlike UVB rays, which are strongest from 10 a.m. These are the rays that tan and age skin, and along with UVB, contribute to skin cancer. UVA rays penetrate the skin more deeply than UVB. ![]() SPF also doesn’t tell you anything about how well the sunscreen protects against UVA rays. The breakdown: SPF 30 blocks 97 percent of UVB rays, SPF 50 blocks 98 percent, and SPF 100 blocks 99 percent. And no sunscreen blocks 100 percent of the sun’s rays. In addition, the intensity and wavelength distribution of UVB rays vary throughout the day and by location. ![]() So you need to reapply every 2 hours, or immediately after swimming or sweating. For example, if you’d normally burn after 20 minutes in the sun without sunscreen, an SPF 30 theoretically protects for 600 minutes, or 10 hours. Once the sunscreen gets on your skin, however, it begins to break down and it can also be rubbed off. Usually the number is explained as the amount of time it takes an individual’s exposed skin to burn when it’s covered in sunscreen compared with when it’s not. The SPF number is a measure of how well a sunscreen protects against sunburn, which is mostly the result of exposure to the sun’s UVB rays. ![]() We also look at how closely the sun protection factor (SPF) listed on the product’s label matches a sunscreen’s average tested SPF. We test sunscreens to determine their effectiveness against the sun’s ultraviolet A and ultraviolet B rays. Still, ideally you want to use a product that you can count on to fully protect your skin. The second most important thing is that any sunscreen is better than none. Here’s the most important thing to know about sunscreen: Everyone 6 months and older, regardless of skin tone, should use it on exposed skin when they head outside (even on cloudy days). ![]()
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