Robust Seawater-Resistant O/W Sunscreen Formulation via Alginate-Cation Crosslinking.

With the growing prevalence of outdoor leisure activities, water resistance has emerged as a critical requirement for sunscreen formulations. Herein, we propose a novel oil in water (O/W) sunscreen formulation with improved moisturizing and water resistance properties by exploiting the ion-responsive crosslinking mechanism of sodium alginate, a natural polysaccharide derived from brown algae. Stable film formation was optimized depending on calcium concentrations and the molecular weight of sodium alginate. In hydration assessments using a molded PMMA plate and a porcine skin model, the hydrogel film functioned as an effective moisturizing barrier, thus reducing water loss. In vivo clinical evaluations demonstrated that the alginate-containing formulation significantly improved water resistance under seawater conditions compared to the control. Collectively, these findings indicate that the developed formulation maintains the favorable sensory characteristics of O/W emulsions while delivering high-performance water resistance particularly optimized for marine environments.