Did you know that SPF 15 blocks 93% of UVB rays; SPF 30 blocks 97% of UVB rays; and SPF 50 blocks 99% of UVB rays? They all can be effective. However, your answer lies in how much you apply and how often. The reality is that an SPF 15 isn’t really a 15 if you only apply a thin layer. Therefore, we urge you to layer your sunscreen. Apply your sunscreen 30 minutes before exposing yourself to the sun. Let it dry down for at least 15 minutes and then reapply another coat just before your tennis match, mountain hike or other outdoor activity. Reapply every two hours to give adequate coverage and every hour if swimming or sweating. That way, you’ll have a fighting chance of achieving the full SPF rating and maximizing the potential UVA protection of your product.
As an FYI, a product’s SPF is measured in a laboratory setting. Subjects put on a certain amount of sunscreen per centimeter of skin and are then exposed to a solar simulator (a lamp that creates UV radiation similar to sunlight). It is important to note that the amount of sunscreen applied for this test is quite heavy, far more than most people ever use at the beach.
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