Phytocosmetic Water-in-Oil Emulsions with Plant Oils: Physicochemical, Rheological and Photoprotective Evaluation

Plant oils are increasingly explored as sustainable functional ingredients in topical emulsions due to their emollient properties and reported photoprotective potential. This study aimed to formulate physically stable W/O emulsions containing selected plant oils (olive, avocado, sesame, flaxseed, and grape seed oils) at two concentrations (15% and 30%) and to evaluate their physicochemical, rheological, occlusive, and UV-protective properties. All formulations were confirmed as W/O systems with skin-compatible pH values and demonstrated shear-thinning, non-Newtonian flow with varying degrees of thixotropy. Increasing oil content from 15% to 30% reduced shear stress, consistency index, and viscoelastic moduli, indicating a softer internal structure. Moreover, the viscosities of the emulsions were not solely determined by the viscosities of the individual oils, suggesting significant interactions with the emulsifier system. High occlusion factors were demonstrated for all emulsions, with the highest values observed for 30% olive- and grape seed oil–based formulations. Spectrophotometric SPF assessment revealed measurable UV-protective activity only for emulsions containing 30% olive, avocado, or flaxseed oil (SPF > 1). All formulations exhibited satisfactory physical stability under mechanical and thermal stress. These findings demonstrate that plant oils can modulate the structure and performance of W/O emulsions and may serve as valuable supportive ingredients in the development of photoprotective cosmetic products.