CHANGING THE RISK SPECTRUM OF INJURY AND THE PERFORMANCE OF SUNSCREENPRODUCTS THROUGHOUT THE DAY

Sunscreen products are tested normally against a defined solar simulat or spectrum that, in ultraviolet (UVB), closely resembles the noontime spectral composition of summer sunlight. Although such a spectrum may define the product for use in the most adverse sunlight conditions, l ittle attention has been given to how such products perform against ot her natural sunlight spectra. Outdoor clinical trials suggest that ind oor testing of sunscreens may overestimate the performance of many pro ducts. In this study we compared the predicted efficacy of specific pr oducts to a variety of natural sunlight spectra taken at different sol ar angles and under different atmospheric conditions. We found that a standard product always provides less protection for a natural sunligh t spectrum than its label value would suggest. The deviation from the labeled value is the greatest when the sun is low in the sky, i.e., cl ose to the horizon. The deviation is due to the changing ratio of UVA to UVB radiation in natural sunlight. The deviation can be as large as a factor of 2.0.