Testing SPF 15–100, Indoor vs. Outdoor

In June of 2011, the U.S. Food and Drug Administration (FDA) published its report, Revised Effectiveness Determination: Sunscreen Drug Products for Over-the-counter Human Use, 21 CFR part 201.1 This stated, “The record does not currently contain sufficient data to indicate that there is additional clinical benefit above SPF 50.” However, the FDA invited submissions for data demonstrating the contrary. In response, this author submitted test data showing that a group of four commercial products with SPFs between 70 and 85 protected individuals better than a group of four commercial products with SPFs from 50 to 55.2

By definition, the FDA’s clinical method1 to test sunscreens indicates an SPF of 100 requires twice as much erythemal UV energy as an SPF 50 to produce the same effect. Yet many argue there is no clinical difference between the two, and that consumers are equally protected by either. In fact, as this article was written, an Internet search for “What SPF is needed?” retrieved three articles in which dermatologists stated: 1. The difference in UVB protection between an SPF 100 and SPF 50 is marginal; far from offering double the blockage, SPF 100 blocks 99 percent of UVB rays, while SPF 50 blocks 98 percent. (SPF 30, that old-timer, holds its own, deflecting 96.7 percent).3 2. It is logical for someone to think that an SPF of 30 is twice as good as an SPF of 15, and so on, but that is not how it works;4 and 3. Actually, an SPF 70 doesn’t protect you that much better than a SPF 30.5

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