An In Vivo Murine Simulated Seaside System for Assessing Sunscreen Efficacy and Durability

Ultraviolet (UV) radiation is a primary environmental factor causing skin photoaging, sunburn, and acute UV-induced skin injury. Sunscreen is the most common method of photoprotection; however, current evaluation methods fail to accurately simulate complex seaside environments or pose high costs and ethical limitations. This study presents a novel simulated seaside testing system combined with a live murine model to quantitatively evaluate the efficacy and durability of sunscreens under complex environmental stressors. The custom-designed chamber integrates controllable UV irradiation, seawater immersion with simulated waves, and wind-drying mechanisms. Depilated BALB/c mice were treated with different sunscreens and exposed to a standardized 120-minute simulated seaside cycle. The retention rate of the sunscreens was quantified using fluorescence imaging, while the photoprotective efficacy was evaluated by Hematoxylin and Eosin (H&E) staining for epidermal thickness and inflammatory infiltration. The results demonstrated that this system could effectively differentiate the performance of various sunscreens. Specifically, a high-protection water-resistant sunscreen exhibited the highest retention rate and provided the best protection against UV and environmental damage. This protocol offers a cost-effective, highly reproducible, and ethical preclinical screening alternative for exploring skin protection products under simulated extreme environments, serving as an exploratory bridge rather than a validated replacement for mandatory human SPF testing.