Background: Covering the skin by topical films affects the skin hydration and transepidermal water loss (TEWL). In vivo studies to investigate the water vapor permeation through topical films are complicated, expensive, ethically not preferred, and time- and labor-consuming. The objective of this study was to introduce an in vitro and subject-independent alternative evaluation method to predict the breathability of topical formulations. Methods: In this study, we developed an in vitro setup to simulate the TEWL values of human skin and investigated the breathability of five polymeric film formers used in topical formulations. Furthermore, a comparative in vivo TEWL study was performed on ten human volunteers with defined areas of skin covered with films of two selected polymers possessing different barrier properties. Results: By employing the in vitro setup, a vinylpyrrolidone/acrylates/lauryl methacrylate copolymer was determined to form the most breathable film, whereas acrylates/octylacrylamide copolymer and shellac films showed the highest barrier properties. The in vivo TEWL study demonstrated the same relative barrier properties for the acrylates/octylacrylamide and polyurethane-64 films, despite a more complex driving force for water vapor permeation due to moisture accumulation on the covered skin surfaces. Conclusion: We obtained a good correlation between the in vitro and in vivo results, demonstrating that our model can categorize different polymeric film formers based on their breathability when applied to human skin. This information can aid in selecting suitable film-forming polymers for topical formulations with either breathable or occluding functionalities.
- film-forming polymers
- skin model
- transepidermal water loss (TEWL)