Evaluating the Efficacy of Sunscreen Formulas in Reducing UV Filter Permeation Into the Stratum Corneum via In Vivo Confocal Raman Spectroscopy: Insights and Applications for Practical Suncare Product Design.

AIMS: The transdermal permeation of UV filters has long been a concern among consumers and researchers. Among them, the permeation of small-molecule UV filters such as homosalate (HMS) (molecular weight < 500 Da) and the regulatory effects of formulation components on its permeation have not been fully investigated. Furthermore, sunscreen formulations containing skin brightening agents have become increasingly prevalent in recent years. Thus, verifying how to adjust formulation components to reduce UV filter permeation while not influencing the permeation of active ingredients such as the skin-brightening agent niacinamide is worthy of research.

METHODS

This study investigated the skin permeation of formulations containing HMS using an improved confocal Raman spectroscopy method.

RESULTS

Among the tested UV filters, HMS exhibited the highest permeation, with a relative permeability rate of 4.2% and a maximum permeation depth of 60 μm. Subsequently, adjusting the proportion of components in the formulation indicated that thickeners (Carbomer and Acrylates/C10-30 Alkyl Acrylate Crosspolymer) and emulsifiers (PEG (Polyethylene Glycol)-100 Stearate/Glyceryl Stearate) could reduce the permeation of HMS, while the film-formers (VP (Vinylpyrrolidone)/Eicosene) had no impact on HMS permeation. Based on these findings, a real-life sunscreen formulation was designed and verified to reduce HMS permeation while ensuring effective skin permeation of niacinamide.

CONCLUSION

The permeation of different single UV filters by confocal Raman spectroscopy suggested that HMS exhibited the deepest permeation. Subsequently, by designing a series of distinct formulations, we identified the formulation components that influence the permeation of HMS. Based on the study findings, a practical formulation was designed that not only minimizes the permeation of the UV filter (HMS) but also does not inhibit the permeation of the skin-brightening agent. This study may serve as a reference for subsequent investigations into the permeation of UV filters.