ABSTRACT
This study focuses on the fate of excipients contained in topical emulsions once applied on the skin. The aim was thus to develop a methodology to characterize the residue left on the skin shortly after emulsion application. To this end, both the role and the impact of the different excipients on the formation and properties of the residue left on the skin surface once a product is applied were investigated. To that purpose, an O/W emulsion composed of an ester as oily phase, an emulsifier (alkylpolyglucoside-based vehicles), a polymer and a humectant (hydrophilic excipient) was first developed. Then, systems with fewer ingredients were prepared to understand their respective role in the residual film. This residual film was studied in vivo by means of biophysical instrumental methods, all being performed on the participants' forearm. Results highlighted the major role of the ester giving a bright and hydrophobic residue. While the surfactant structuration as the presence of glycerin and polymer provided a specific water distribution inside the residue on the skin surface. Finally, this work evidenced the ingredients organization in the residue depending on the systems composition, with a particular stratification on skin surface which could be considered in the formulation strategy for efficient active delivery and skin protection.
