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Sunscreen Efficacy

By: Elsa Jungman, University of Paris XI, and Howard I. Maibach, MD, University of California
Posted: July 27, 2010, from the August 2010 issue of GCI Magazine.

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In the 1999 US Food and Drug Administration (FDA) monograph, the same time periods were required for a sunscreen to be labeled as water resistant or very water resistant; however, the final SPF level indicated on the label is the SPF measured after the last immersion and there is no comparison with the SPF level before water cycles. Therefore, water resistance tests are different in the United States and Europe and a manufacturer must conduct different tests to claim water resistance in both countries. As a result, the same product may show different claims on its label depending upon where it is being sold.

Sunscreens can be less efficient during outdoor sports due to water exposure, sweat and friction, so participants of outdoors sports require high levels of sun protection. Even tan athletes who use sunscreen get sunburn. Ambros-Rudolph et al. have shown that melanoma risk increases in marathon runners due to UV exposure and immunosuppression.

UV exposure was assessed on the backs of three athletes involved in an Iron Man competition. The athletes wore a UV spore detector and an SPF 25 water resistant sunscreen. Despite the UV filter, however, burn was visible at the race’s end. It is possible that the sunscreen was washed off by the sea water and/or sweating; it also was not indicated whether the athletes reapplied sunscreen during the race.


Since studies have shown that consumers apply far less sunscreen than that used in SPF evaluations, the SPF achieved is often half of what is labeled. Sunscreens are also spread onto small areas and many anatomic sites are missed. Thus, it is recommended that consumers be educated to understand how to appropriately apply sunscreens.

In addition, it was found that consumers typically apply more sunscreen when it is packaged in a large-mouthed jar. It is therefore recommended that manufacturers observe consumer behavior when designing sun product packaging. Offering sunscreen in a jar could permit consumers to better judge the amount applied.