Instrumental and sensory methodologies to characterize the residual film of topical products applied to skin.

BACKGROUND: The work is aimed at the development of a methodology to characterize the tactile properties of topical products during application. Specific attention was paid to the study of the residual properties left at the surface of the skin. This approach was interestingly used to better understand the formulation factors governing the skinfeel of topical preparations. MATERIALS AND METHODS: Cosmetic and pharmaceutical topical products were selected based on their various texture, galenic form (gel or emulsion), and composition (polymer used as texturing agent). Key texture attributes namely Firmness, Stickiness, Spreadability, and Amount of residue were objectively evaluated using sensory analysis. Additionally, texture analysis (compression test), rheology (flow test), and tribology (in vivo friction test) were carried out. RESULTS: Sensory evaluations highlighted a great diversity of tactile properties among products when applied to skin. For example, assessors perceived an important amount of residue left by emulsions whereas gels were not leaving any residue after application to the skin. These results were confirmed by in vivo tactile friction measurements with two distinct evolutions in time of the residual film properties. CONCLUSION: The present investigation shows how the tactile properties of topical gels and emulsions are studied using complementary tests in order to understand and improve the skinfeel of topical preparations.