Standardized In Vivo Method Using High-Resolution Diffuse Reflectance Spectroscopy for Evaluating Sunscreen...

Accurate and reliable evaluation of sunscreen performance is necessary to ensure adequate balanced sun protection against ultraviolet light (UV) and high-energy visible light (HEV), depending on an individual's skin phototype and dermatoses. The objective of this study was to investigate the importance of methodological considerations for standardized evaluation of sunscreen performance to protect against UVA, especially long UVA1, and HEV.

In an open in vivo study, 6 commercial sunscreens were applied on the backs of subjects (n = 15) to evaluate the performance against UVA and HEV using a robust protocol of hybrid diffuse reflectance spectroscopy (HDRS), based on validated ISO methodology. High-resolution absorbance spectra were obtained between 310 and 450 nm using a 1 nm stepsize. The region 365-450 nm was compared with a method using linear interpolation from four discrete wavelengths (365, 405, 435 and 450 nm).

The sunscreen ranking observed using the in vivo high-resolution spectral representation (1 nm steps) method was not consistently reproduced by the method using four discrete wavelengths with linear interpolation. Differences between the two methods were observed in the range of 380-400 nm, leading to misclassification in the rank of protection depending on the methodology used.

The absorption profile in the UVA and HEV light ranges of each sunscreen was determined accurately and reliably by diffuse reflectance spectroscopy with measurements every nanometer. Sunscreen performance characterization will depend on the methodology, and applying linear interpolation from broader wavelength bands may give inaccurate results.