The present invention relates to methods for an objective and quantitative erythema documentation and analysis. In particular, the invention relates to a method for assessing erythema of a subject comprising the steps of measuring the light reflectance of a skin or mucosal area of the subject, obtaining the L* value and the a* value of said measurement according to the L*a*b* color space, and calculating the erythema value according to the formula (L*max−L*)×a*.