COMPARISON OF THE PHOTOPROTECTIVE EFFECTS OF SUNSCREENS USING SPECTROPHOTOMETRIC MEASUREMENTS OR THE SURVIVABILITY OF YEAST CELLS EXPOSED TO UV RADIATION

Abstract

This work focuses on simple methods that allow comparison of the photoprotective effects of sunscreens. One such method described by Mansur and colleagues relies on the spectrophotometric measurements of the organic filters extracted with ethanol. The extracts are subjected to absorbance measurements in the of 290 to 320 nm range, with 5 nm intervals. The sunscreen sun protection factor (SPF) is estimated with an equation that relates each absorbance value with their respective erythemal effect, at the wavelength used for each measurement. In the current work, three commercial sunscreens were assayed using this method, which produced SPF values that were markedly lower than those declared by the manufacturers. These results prompted a more thorough analysis, which concluded that the Mansur method is not suitable for assaying sunscreens with SPFs above 15. The analysis included a survey of the data previously reported by several authors that had used the same method. On the other hand, this report also includes the optimization of a yeast serial dilution assay that allows reliable comparison of the photoprotection levels conferred by sunscreens. Importantly, this yeast assay could be applied to compare the photoprotective effects of products with a wide range of SPFs, including sunscreen lotions, filter suspensions or solutions, natural product extracts, etc.