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Sunscreen Efficacy

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

This is an excerpt of the Cosmetics & Toiletries magazine feature "Enhancing Sunscreen Efficacy for Realistic Application," originally printed in C&T's July 2010 issue . All references are cited in the C&T feature.

Both UVA and UVB solar radiation can cause skin damage, and while sunscreens contain organic or physical UV filters to protect the skin from sunburn, questions remain as to the role of sunscreens in preventing melanoma. However, the association made between lack of sunscreen use and melanoma risk may relate to individuals who remain in the sun for long periods of time without seeking shade and/or wearing sunscreen, protective clothing and hats.

The ability of a sunscreen to protect the skin from erythema is expressed on product labels as the sunburn protection factor (SPF). Yet, in reality, consumers do not apply the same mass/cm as is utilized in SPF testing, so maximal protection is not achieved. In addition, other factors interfere with sunscreen efficacy, including reapplication, sweat and water resistance, formulation and packaging.

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). 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.

Water Resistance; Outdoor Sports Use

Guidelines for evaluating a sunscreen’s water resistance were devised by Coloipa, the European cosmetics association, in December 2005. Sunscreen is applied to the backs of volunteers at a dosage of 2 mg/cm, 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 brand owner 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; 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.


Some experts have recommended changing the amount of sunscreen used for SPF testing in order to adapt to real life usage conditions. While the FDA considered public comments and data/information brought to its attention and proposed a rule to amend the Final Monograph for OTC sunscreens in August 2007, the rule did not include a proposed method change. This was not only because the group believes that lowering the sunscreen density is not necessary to more accurately test for sunburn protection, but also because changing the amount of sunscreen used for SPF testing implies international coordination toward a globalized method and labeling requirements.

Instead, the FDA prefers that product labels encourage consumers to apply a thicker layer. Manufacturers can select one or more of the following terms: liberally, generously, smoothly or evenly. In addition, it would be beneficial for sunscreen labels to direct consumers to: apply to all skin exposed to the sun, serving as a reminder that all uncovered anatomic sites are exposed to UV. No sweat resistance testing was proposed in the new FDA monograph either, which could be important for individuals practicing outdoor exercise.

Finally, the efficacy of day care and makeup products containing UV filters should also be investigated. Foundations are applied in thinner layers and the protection achieved is likely far from the SPF level indicated on the label. A special SPF test should exist for such makeup and moisturizers that incorporate UV filters.

Sunscreen application and use have become highly efficient but educational messages to the consumer require further development. Besides learning to apply the right amount, consumers must also understand that wearing sunscreen does not mean they should spend longer periods of time in the sun. In addition, sunscreen should not be used as the primary prevention but as a complement to shade, clothing and broad-brimmed hats.

A complete list of references is available here.

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