Relative Action of Sunscreen Compounds

Abstract

A simple and rapid method of evaluating the relative screening action of sunscreen compounds is given. The optical density of a 0.1 per cent solution in a 0.1-mm. fused silica cell is measured at 3,080 Ångströms, the peak of the “Sunburn Curve.” The optical density is divided by the per cent concentration, thus reducing all values to those given by a 1 per cent solution. These values are termed the sunscreen index (S.I.) of the compounds. Values of the sunscreen index are given for 45 compounds. An example is given showing how the sunscreen index may be used to calculate what per cent of any of the compounds is needed in a given thickness of film to screen out any given per cent of the light which produces sunburn.