Sunscreen applied at ≥2 mg cm-2 during a sunny holiday prevents erythema, a biomarker of ultraviolet radiation-induced DNA damage and suppression of acquired immunity

BackgroundSun protection factor (SPF) is assessed with sunscreen applied at 2 mg cm(-2). People typically apply around 08 mg cm(-2) and use sunscreen daily for holidays. Such use results in erythema, which is a risk factor for skin cancer. ObjectivesTo determine (i) whether typical sunscreen use resulted in erythema, epidermal DNA damage and photoimmunosuppression during a sunny holiday, (ii) whether optimal sunscreen use inhibited erythema and (iii) whether erythema is a biomarker for photoimmunosuppression in a laboratory study. MethodsHolidaymakers (n = 22) spent a week in Tenerife (very high ultraviolet index) using their own sunscreens without instruction (typical sunscreen use). Others (n = 40) were given SPF 15 sunscreens with instructions on how to achieve the labelled SPF (sunscreen intervention). Personal ultraviolet radiation (UVR) exposure was monitored electronically as the standard erythemal dose (SED) and erythema was quantified. Epidermal cyclobutane pyrimidine dimers (CPDs) were determined by immunostaining, and immunosuppression was assessed by contact hypersensitivity (CHS) response. ResultsThere was no difference between personal UVR exposure in the typical sunscreen use and sunscreen intervention groups (P = 008). The former had daily erythema on five UVR-exposed body sites, increased CPDs (P < 0001) and complete CHS suppression (20 of 22). In comparison, erythema was virtually absent (P < 0001) when sunscreens were used at 2 mg cm(-2). A laboratory study showed that 3 SED from three very different spectra suppressed CHS by around 50%. ConclusionsOptimal sunscreen use prevents erythema during a sunny holiday. Erythema predicts suppression of CHS (implying a shared action spectrum). Given that erythema and CPDs share action spectra, the data strongly suggest that optimal sunscreen use will also reduce CPD formation and UVR-induced immunosuppression.