Enhancing Sunscreen Efficacy for Realistic Application

By: Elsa Jungman, University of Paris XI, and Howard I. Maibach, MD, University of California

Posted: June 30, 2010, from the July 2010 issue of Cosmetics & Toiletries.

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Sunscreen Packaging
Lynfield and Schechter compared the application amount of four preparations: an o/w emulsion, an ointment, a liquid with an alcoholic phase (sunscreen), and an o/w suspension (sunscreen).⁷ The researchers used 29 volunteers, 15 men and 14 women, who applied each formulation as if it was a cream outside the bathing suit and scalp area. The researchers found that even when 30% of the body was skipped with the alcoholic solution, there was no difference in amount applied with the various formulations. The cream was given to the volunteers both in jar and tube packaging. When the sunscreens were dispensed in a small tube or a large-mouthed jar, the amount applied differed. Specifically, application of the emulsion from a jar was “wasteful,” whereas sunscreen in a tube was applied sparingly. When the sunscreen was applied from a jar, the amount approximated 24 g, which is closer to the amount required to cover the entire body (35 g), whereas only 10 g of the same formulation was applied from the tube.1, 6

Water, Sweat Resistance
Guidelines for evaluating a sunscreen’s water resistance were devised by Coloipa, the European cosmetics association, in December 2005.¹⁰ Sunscreen is applied to the backs of volunteers at a dosage of 2 mg/cm², the sunscreen is dried for 15 min to 30 min, and the SPF is measured. The volunteer’s back is then immersed in water for two periods of 20 min and dried for 15 min after each immersion. The SPF is measured again 15 min after the last water immersion. To claim water resistant, the SPF measured must be equal or greater than 50% of the SPF level measured before water immersion. For a manufacturer to claim extra water resistant, the test is conducted for four periods of 20 min. No toweling is allowed during the procedure.

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;¹¹ 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.

With regard to the eccrine sweat resistance of sunscreens, no protocol has yet been published to test for it. However, the FDA allows water resistant sunscreen to be labeled as sweat resistant, which is most likely a marketing strategy.

Sports Activities
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.¹²