A method for broad spectrum classification of sunscreens

Synopsis A method is described and evaluated for classifying sunscreen products into different broad spectrum categories. The method is based on spectrophotometric analysis of products applied to a suitable substrate and obviates the need for human or animal studies utilizing clinical endpoints which may be of dubious value in relation to protection from sun exposure. The absorbance spectrum obtained by spectrophotometric assay is reduced to a single index by determining that wavelength lambda(c) where the area under the spectrum from 290 nm (the approximate lower wavelength limit of terrestrial sunlight) to lambda(c) is 90% of the integral of the absorbance spectrum from 290 to 400 nm. A five-point scale is used to classify products as follows: The method makes no underlying assumptions about the form of action spectra for either acute or chronic photobiological damage. However, acknowledgement is made of the fact that the efficiency of ultraviolet radiation to induce a given photobiological endpoint tends to decrease with increasing wavelength by adopting wavelength intervals for classifying the Broad Spectrum Rating which increase in an approximately logarithmic manner.