Development and Physicochemical Characterization of an Argan–Castor Oil O/W Emulsion for Cosmetic Applications

The incorporation of plant-derived oils into cosmetic formulations has attracted increasing interest due to their natural origin, skin compatibility, and multifunctional formulation roles. Argan and castor oils are widely used in cosmetic products as emollient lipid components with intrinsic antioxidant properties. However, limited studies have systematically evaluated the physicochemical stability and antioxidant performance of emulsions combining these two oils. The aim of this study was to develop and comprehensively characterize a stable oil-in-water (O/W) cosmetic emulsion based on argan and castor oils using a natural non-ionic emulsifier (C14–22 Alcohol (and) C12–20 Alkyl Glucoside). Particular emphasis was placed on formulation stability, as it represents a critical prerequisite for further product evaluation. Stability was investigated through thermal stress testing (4–37 °C), centrifugation assays, droplet size analysis, and zeta potential measurements. Complementary physicochemical and structural characterization was performed using rheological analysis and Fourier transform infrared (FT-IR) spectroscopy. The formulated emulsion exhibited good physical stability with no phase separation under the tested conditions, a skin-compatible pH, a uniform droplet size distribution (4.15 ± 0.68 µm), and pseudoplastic, moderately thixotropic rheological behavior. Antioxidant capacity was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, yielding an IC50 value of 19.21 ± 1.02 mg/mL. Overall, this study provides a formulation-oriented framework for the development and evaluation of stable natural oil-based O/W emulsions intended for cosmetic applications, supporting future optimization and biological validation.