Sub-optimal Application of a High SPF Sunscreen Prevents Epidermal DNA Damage in Vivo

Abstract

The cyclobutane pyrimidine dimer (CPD) is a potentially mutagenic DNA photolesion that is the basis of most skin cancers. There are no data on DNA protection by sunscreens under typical conditions of use. The study aim was to determine such protection, in phototypes I/II, with representative sunscreen-user application. A very high SPF formulation was applied at 0.75, 1.3 and 2.0 mg/cm2. Unprotected control skin was exposed to 4 standard erythema doses (SED) of solar simulated UVR, and sunscreen-treated sites to 30 SED. Holiday behaviour was also simulated by UVR exposure for 5 consecutive days. Control skin received 1 SED daily, and sunscreen-treated sites received 15 (all 3 application thicknesses) or 30 (2.0 mg/cm2) SED daily. CPD were assessed by quantitative HPLC-tandem mass spectrometry (HPLC-MS/MS) and semi-quantitative immunostaining. In comparison with unprotected control sites, sunscreen significantly (p ≤ 0.001-0.05) reduced DNA damage at 1.3 and 2.0 mg/cm2 in all cases. However, reduction with typical sunscreen use (0.75 mg/cm2) was non-significant, with the exception of HPLC-MS/MS data for the 5-day study (p <0.001). 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.

Incidence and public health burden of sunburn among beachgoers in the United States

“…Additionally, sunscreen application is often considerably less than the amount recommended (2 mg/cm 2 ) by the U.S. Food and Drug Administration (FDA) (U.S. Food and Drug Administration, 2012). A study among beachgoers (Lademann et al, 2004) found that volunteers typically applied only 10% of the recommended amounts, with the ears and top of the feet mostly remaining unprotected and a recent study (Young et al, 2018) found that sunscreen applied at 0.75 mg/cm 2 , was not effective in reducing DNA damage from UVR exposure. Currently, the FDA requires sunscreen labeling stating that sunscreen should be used in combination with other sun protective measures, such as the use of shade or protective clothing (U.S. Food and Drug Administration, 2012).…”

Sunscreen applied at ≥ 2 mg cm−2during a sunny holiday prevents erythema, a biomarker of ultraviolet radiation‐inducedDNAdamage and suppression of acquired immunity

“…We have reported that sunscreens can prevent the accumulation of thymine dimers from repeated daily suberythemal SSR exposure . We have also shown that a high‐SPF sunscreen can prevent DNA damage caused by acute and repeated high‐dose SSR exposure . However, there are very limited data on the relationship between SPF and DNA protection factor.…”

Consensus statement from 2nd International Conference on Controversies in Vitamin D

“…Sunscreens are effective because they attenuate solar UVR. Their use can inhibit cyclobutane pyrimidine dimers (CPDs) [68], sunburn and skin cancer [69]. The sun protection factor (SPF) of a sunscreen is primarily an index of its ability to attenuate UVB [70].…”