Abstract: A method is disclosed for evaluating erythema utilizing skin reflection measurements. By collecting and analyzing data representative of both normal and erythematous skin utilizing reflectance spectra within a range of 400 to 700 nm, distinctive spectral features of erythema have been identified. A relationship representing a function of normal and erythematous skin reflectance at three specific wavelengths (500 nm, 550 nm, and 595 nm) was developed to provide an absolute measure of the vascular response of the skin, which measure is independent of pigmentation characteristics of the skin and takes into consideration normal fluctuations in skin color. By varying the exposure of the skin to radiation from a predetermined source and then measuring the reflectance of the skin at particular time periods and at a plurality (preferably three) of different wavelengths, the relative changes in superficial blood volume due to erythema are isolated.