The feasibility of using fluorescence spectroscopy as a rapid, non-invasive method for evaluating sunscreen performance.

We have carried out ex vivo studies to examine the feasibility of using fluorescence spectroscopy as an in vivo quantitative technique to assess sunscreen substantivity in terms of skin surface thickness and/or photoprotection. We found that the majority of sunscreens produced insufficient natural fluorescence and so we have attempted to increase the fluorescent signal by adding various fluorescing agents to the sunscreens. However, none of these substances is ideal; either they do not bind sufficiently strongly to sunscreen products, or their fluorescence is quenched by the active ingredients contained within sunscreens. The feasibility of using fluorescence spectroscopy for in vivo quantitative assessments of sunscreen substantivity therefore remains unproved and is dependent on a suitable fluorescent agent being found. Such an agent would have to be non-toxic, mix readily with sunscreens and be excited by visible wavelengths.