A diffuse reflectance spectroscopy (DRS) method can quantify skin barrier function and hemoglobin concentration, thereby improving severity evaluation in psoriasis vulgaris, according to a study pulished in Scientific Reports. Noting that researchers utilize instruments that measure transepidermal water loss and skin capacitance to investigate skin barrier function and assess severity in psoriasis vulgaris, Chao-Kai Hsu, MD, PhD, and colleagues used a custom-built DRS system, shown to be able to determine skin water-protein binding status and the hemoglobin concentration and performed cross-validation of DRS measurement results with readings derived from the Courage + Khazaka Corneometer and Mexameter and Psoriasis Area and Severity Index (PASI) scores. The Mexameter erythema readings were a good representation of skin oxygenated hemoglobin but not deoxygenated hemoglobin. However, dermatologists in this study were inclined to rate the “erythema” category with higher scores as the level of the skin deoxygenated hemoglobin was higher. Consequently, Mexameter-derived erythema readings may not be concordant with the PASI erythema scores.