Comparative Study Between Nanoemulsions and Conventional Emulsions as Carriers of Plant Oils: Formulation Approach, Physicochemical Properties, and In Vitro and In Vivo Assessments for Skin Care Application

This study aims to compare nanoemulsions and conventional emulsions as delivery systems for plant oils. For this reason, the formulation approach was evaluated, followed by an assessment of physicochemical properties and stability. Six different compositions of emulsions and their respective nanoemulsions were prepared using combinations of solid lipids (beeswax or cocoa butter) with liquid lipids (olive, almond, or apricot oil). Their physicochemical characteristics and their colloidal stability over time were assessed using Dynamic Light Scattering or Static Light Scattering. The performance of samples on the skin was assessed by measuring their occlusion effect (F), while their hydrating effect was assessed on healthy volunteers. The nanoemulsions exhibited improved stability compared to the corresponding conventional emulsions of the same composition. However, all samples (emulsions or nanoemulsions) exhibited a satisfactory occlusive effect (F > 10), mainly at 6 h. In addition, all samples caused increased skin hydration by 10–20% one hour post-application. Nanoemulsions containing plant-origin oils showed better physicochemical stability compared to their corresponding emulsions. The in vivo assessment revealed no skin irritation caused by the samples. Nevertheless, subjective evaluations by volunteers unveil a preference for conventional emulsions, which were perceived as providing a more favorable skin texture, regardless of their composition.