LAUSR

Background: The value of additional photoprotection provided by use of high–sun protection factor (SPF) sunscreens is controversial, and limited clinical evidence exists. Objective: To compare the sunburn protection provided by SPF 100+ and SPF 50+ sunscreen in conditions of actual use. Methods: A total of 199 healthy men and women (≥18 years) participated in a natural sunlight, single‐exposure, split‐face, randomized, double‐blind study in Vail, Colorado. Each participant wore both sunscreens simultaneously during activities, with no use restrictions other than designation of the treatment area. Erythema was clinically assessed on the day following exposure. Comparative efficacy was evaluated through bilateral comparison of sunburn between treatment areas and erythema score, as evaluated separately for each treatment area. Results: Following an average 6.1 ± 1.3 hours of sun exposure, investigator‐blinded evaluation identified 55.3% of the participants (110 of 199) as more sunburned on the SPF 50+ protected side and 5% (10 of 199) on the SPF 100+ protected side. After exposure, 40.7% of the participants (81 of 199) exhibited increased erythema scores (by ≥1) on the SPF 50+ protected side as compared with 13.6% (27 of 199) on the SPF 100+ protected side. Limitations: Single‐day exposure may not extrapolate to benefits of longer‐term protection. Conclusion: SPF 100+ sunscreen was significantly more effective in protecting against sunburn than SPF 50+ sunscreen in actual use conditions.