Study shows the best way to apply sunscreen to reduce the risk of skin cancer.

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This was an in vivo study investigating the effect of sunscreen application in preventing human skin DNA damage that potentially is the basis for most skin cancers. A sunscreen with a very high level of UV protection (SPF 50+) was applied to 16 healthy young subjects with Fitzpatrick skin phototypes I and II.  Sunscreen was applied at thicknesses of 0.75, 1.3 and 2.0 milligrams per square centimetre of skin (mg/cm²). The volunteers were split into two exposure groups; a group that received a single UV radiation exposure (acute exposure group) and a group that received a daily UV radiation exposure for 5 consecutive days (repeated exposure group).  UV radiation exposure was provided artificially with characteristics closely matching sun exposure. The acute exposure group received 30 standard erythema doses (SED) per sunscreen application thickness. The repeated exposure group received 15 SEDs daily for all application thicknesses to simulate a typical holiday exposure at a tropical latitude. The repeated exposure group also received 30 SEDs daily at an additional site with a 2 mg/cm² sunscreen thickness. Unprotected skin was exposed to 4 SEDs in the acute exposure group and 1 SED daily in the repeated exposure group for experimental control.

The authors reported that sunscreen significantly reduced DNA damage at application thicknesses of 1.3 and 2.0 mg/cm². Application thickness of 0.75 mg/cm², representative of typical application, was only significant in reduction of DNA damage in the repeated exposure group.

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The study showed that the use of a very high SPF factor sunscreen can inhibit DNA damage in human skin caused by exposure to UV radiation. Although typical sunscreen application showed some value in providing UV protection in people going out in the sun for consecutive days, the importance of better sunscreen application was supported by the reduction of DNA damage in going out in the sun on occasion.

Overall, the results reported by the authors support ARPANSA’s sun protection messaging. Further, the study emphasises the importance of communicating the most appropriate way to apply sunscreen to offer the best protection outcomes.