Rational Selection of Phytochemical Mixtures for Sunscreen Development Based on in vitro Efficacy and Cytotoxicity Profiles

This study evaluated combinations of hydroalcoholic plant extracts and purified phytochemicals to identify safe and effective candidates for sunscreen formulations. Fourteen extract–compound mixtures were tested for in vitro photoprotective efficacy and cytotoxicity in MRC-5 human fibroblasts. One mixture comprising Posoqueria latifolia (Rudge) Schult., Rubiaceae, extract (250 mg/ml) and kaempferol (349 µM) demonstrated photoprotective effects while remaining non-cytotoxic, preserving more than 70% cell viability following UVB irradiation. This mixture was subsequently evaluated in an in vivo murine model, in which it exhibited superior erythema protection efficacy (EPE = 41 ± 0.0) relative to titanium dioxide and kaempferol alone. These results support the selection of P. latifolia combined with kaempferol as a promising, safe, and potent natural candidate for photoprotective cosmetic formulations.