Beach vacations are high-risk settings for overexposure to ultraviolet radiation. To compare the sunburn protective efficacy of SPF 50+and SPF 100+sunscreens under actual use at the beach. A prospective, randomized, double-blind, single-center, split-body/face study of 55 healthy individuals. Each participant applied both sunscreens to randomized sides of the face/body for up to 5 consecutive days. Blinded clinical evaluation of erythema by a single grader and objective instrumental assessments, colorimetry, and diffuse reflectance spectroscopy were performed the morning after each sun exposure. After 5days, 31 (56%) participants had more sunburn on the SPF 50+side compared to 4 (7%) on the SPF 100+side. Overall, mean erythema intensity showed statistically significantly less erythema on the SPF 100+side compared with the SPF 50+side. The first observation of sunburn exclusively on the SPF 50+side occurred after 1day of sun exposure, whereas that for SPF 100+occurred after 3days of sun exposure. Only initial sunscreen application was monitored, only 1 participant with skin phototype I was recruited, and participants were recruited from a local beach area. SPF 100+was significantly more effective in protecting against ultraviolet radiation-induced erythema and sunburn than SPF 50+in actual use in a beach vacation setting.