Typical sunscreen application, which is about 0.75 mg/cm2 in thickness, does not offer enough protection for consumers, according to the findings of a recent study.
Manufacturers evaluate the efficacy of sunscreen based on application thickness of 2mg/cm2. To determine whether consumers receive the same benefit at lower levels of thickness, the researchers collected biopsies from 16 participants with Fitzpatrick phototype skin I and II who underwent ultraviolet radiation exposure to simulate sunlight.
One group of participants (n=8) applied high SPF sunscreen at thicknesses of 0.75, 1.3, and 2 mg/cm2 and received a single UVR exposure. The other group received 5 consecutive days of exposure, to mimic vacation behavior, with varying degrees of UVR similar to popular vacation destinations, such as Florida. Damage to DNA, including cyclobutene pyrimidine dimer, was assessed using quantitative liquid chromatography/tandem mass spectrometry and semi-quantitative immunostaining.
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Compared with unprotected skin, skin with sunscreen applied at thicknesses of 1.3 and 2 mg/cm2 had significantly reduced DNA damage. However, sunscreen applied at 0.75 mg/cm2 thickness was not associated with significant reductions in damage except during the 5-day period.
“Overall, these results support sunscreen use as a strategy to reduce skin cancer, and demonstrate that public health messages must stress better sunscreen application to get maximal benefit,” the researchers concluded.
Young AR, Greenaway J, Harrison GI, et al. Sub-optimal application of a high SPF sunscreen prevents epidermal DNA damage in vivo [published online before print July 25, 2018]. Acta Dermato Venereologica. doi:10.2340/00015555-2992