BackgroundLong-term sun exposure is one of the risks faced by outdoor swimmers and can cause sunburn. Using sunscreen is one way to prevent sunburn; however, physical activity can trigger sweat, friction, and water washing that can interfere with sunscreen efficacy and decrease its sun protection factor (SPF). Sunscreens are classified into inorganic and organic based on their filter. Organic sunscreen has a better bond to the skin than inorganic sunscreen, which forms a barrier above the skin layer that makes removing it easier. Organic sunscreen lasts longer than inorganic sunscreen when used in physical activities, but it has a limited spectrum, is more photolabile, and is more allergenic.ObjectiveThis study aims to evaluate the persistency of SPF 30 between inorganic and organic sunscreens on the back area after 1.5 hours of swimming.MethodsThis study is a randomized, split-body, double-blind clinical trial to evaluate the persistency of SPF 30 of the inorganic versus organic sunscreens in swimmers. Randomization was done to allocate the participants into treatment groups. Each participant received inorganic and organic sunscreen treatments applied to the back area. The research participants were swimmers from the Cikini swimming pool and Bina Taruna swimming pool, both in Jakarta, Indonesia.ResultsA total of 22 swimmers were enrolled in this study. The analysis showed no significant difference between the SPF of the two sunscreens before swimming (P=.22). After swimming, the SPF levels of both sunscreens decreased: the inorganic sunscreen decreased from a median of 27 (range 23-47) to 12.3 (range 8-19), and the organic sunscreen decreased from a median of 30 (range 24-47) to 9.9 (range 6-19), which was statistically significant (P<.001). When comparing the SPF of inorganic and organic sunscreens after swimming, there was a statistically significant difference in the decrease in SPF levels between the two groups (P=.02), which indicated a better SPF persistence for inorganic sunscreens when compared to organic sunscreens.ConclusionsThere was a decrease in the SPF levels of inorganic and organic sunscreens after 1.5 hours of swimming, with better persistence in inorganic sunscreens compared to organic sunscreens.Trial RegistrationClinicalTrials.gov NCT04618536; https://clinicaltrials.gov/ct2/show/NCT04618536International Registered Report Identifier (IRRID)RR2-10.2196/42504