Determination of Minimal Erythema Dose and Anomalous Reactions to UVA Radiation by Skin Phototype

Abstract

BackgroundPhototesting is a technique that assesses the skin's sensitivity to UV radiation by determining the smallest dose of radiation capable of inducing erythema (minimal erythema dose [MED]) and anomalous responses to UV-A radiation. No phototesting protocol guidelines have been published to date. MethodologyThis was a multicenter prospective cohort study in which 232 healthy volunteers were recruited at 9 hospitals. Phototests were carried out with solar simulators or fluorescent broadband UV-B lamps. Each individual received a total of 5 or 6 incremental doses of erythemal radiation and 4 doses of UV-A radiation. The results were read at 24hours. ResultsAt hospitals where solar simulators were used, the mean (SD) MED values were 23 (8), 28 (4), 35 (4), and 51 (6)mJ/cm2 for skin phototypes i to iv, respectively. At hospitals where broadband UV-B lamps were used, these values were 28 (5), 32 (3), and 34 (5)mJ/cm2 for phototypes ii to iv, respectively. MED values lower than 7, 19, 27, and 38mJ/cm2 obtained with solar simulators were considered to indicate a pathologic response for phototypes i to iv, respectively. MED values lower than 18, 24, and 24mJ/cm2 obtained with broadband UV-B lamps were considered to indicate a pathologic response for phototypes ii to iv, respectively. No anomalous responses were observed at UV-A radiation doses of up to 20J/cm2. ConclusionsResults were homogeneous across centers, making it possible to standardize diagnostic phototesting for the various skin phototypes and establish threshold doses that define anomalous responses to UV radiation.