Essential Oil‐Based Microemulsion With ZnO and TiO ₂ Lipid Coated‐Nanoparticles for Topical Sunscreen, Mosquito Repellent and Antioxidant Activities

ABSTRACT This study aimed to develop, through a low‐energy process and biocompatible materials, a novel topical microemulsion combining inorganic UV filters and selected essential oils to provide multifunctional protection, including sunscreen, insect repellent, and antioxidant activities as a sustainable alternative to conventional systems based on organic UV filters and synthetic repellents. An oil‐in‐water microemulsion was formulated using 8% (w/w) of an essential oil blend (citronella, lemongrass, basil, and lavender) combined with vitamin E, 30% (w/w) of a 2:1 Eco‐Tween 80/ethanol mixture, and 62% (w/w) water. Lipid‐coated ZnO and TiO₂ nanoparticles (10% w/w), including zinc oxide coated with stearoyl glutamic acid and polyhydroxystearic acid, and titanium dioxide coated with alumina and jojoba esters, were incorporated. Physicochemical parameters, as Z, PdI and pH, among others, were determined. The formulation was evaluated for in‐vitro sun protection factor (SPF), photostability in the UVA range, mosquito repellency against Culex Pipiens pipiens , antioxidant capacity via DPPH assay, and cytotoxicity in HEK293 cells. The developed system displayed a hydrodynamic diameter of 806 ± 74 nm, a polydispersity index of 0.323 ± 0.141, and a pH of 7.83 ± 0.02, indicating suitability for topical application. The formulation demonstrated an in‐vitro SPF of 5.76 ± 0.89 and exhibited stability under the UVA range. Repellency assays showed a repellency index of 0.31, with significant activity sustained for up to 4 h. Moderate antioxidant activity was observed in the DPPH assay, and no cytotoxic effects were detected in HEK293 cells derived from human embryonic renal epithelium, commonly used for toxicity testing of nanomaterials and drugs.