Prediction of minimal erythema dose with a reflectance melanin meter

The relationship between skin pigmentation and sensitivity to ultraviolet (UV) radiation-induced erythema was investigated in 60 healthy subjects of sun-reactive skin types I-V. Using a portable reflectance spectrometer, skin pigmentation was measured as the 'melanin index' (MI) in all subjects. A solar-simulated array of filtered UVA and UVB-emitting fluorescent lamps was then used to determine the UVB minimal erythema dose (MED) of each subject. MI readings and MED testing were both performed on the subjects' mid to upper backs. Using this technique, we found a close correlation between MI and MED. Comparison of the mean MI or MED of subjects with different skin types revealed progressive differences in MI and MED between all five skin types. Erythema dose-response curves, which provide further information about UV sensitivity, were also calculated for 43 subjects. A significant negative correlation was found between the gradients of these curves and both MI and MED, indicating that paler subjects respond more strongly to increments of UV above the MED than subjects with greater pigmentation. Our results indicate that although traditional, subjective means of predicting UV sensitivity to erythema are not without some value, MED correlates particularly strongly with objective measures of skin pigmentation. We therefore conclude that the reflectance spectrometer can rapidly and accurately predict UVB sensitivity, and should prove clinically useful for planning and optimizing UVB phototherapy.