An equation is proposed to link the Cumulative Radiation Effect (CRE) scale of radiation damage with the fraction of basal cells surviving after irradiation of skin epithelium. The model assumes an expression for the basal cell survival curve which fits the various hit-target models over the range of doses found in clinical practice. The model is consistent with CRE in the dependence on total treatment dose and fractionation number. A 'first order' analysis using a Gompertzian re-growth of cells also yields reasonable agreement with the CRE equation in time dependence during treatment and during a gap. This model is suitable for acute skin reactions but not necessarily for late effects in connective tissue.