Ultraviolet-induced inflammation: Validation of the PI-MED erythema measure and its associations with anhedonia

Abstract Affective immunology of the skin is a growing area; however, investigations are limited by the lack of an established protocol for measuring individual differences in cutaneous inflammation. To address this gap, we present a preliminary validation of Precision Implementation of Minimal Erythema Dose (PI-MED) testing as a method for measuring cutaneous inflammation. PI-MED is a recently adapted protocol, optimized for reproducibility and individual differences research, that uses ultraviolet (UV) light to evoke cutaneous erythema, or inflammatory skin reddening. PI-MED’s novel UV dosage schedule produced reasonably standardized erythema responses across different skin pigmentation types, showed strong internal consistency within person, and good test-retest reliability across 8–10 weeks. In line with predictions, increased PI-MED erythema was associated with heightened anhedonia, across several anhedonia measures, beyond the influence of non-affective covariates. While future work should further refine the PI-MED dosage schedule for the lightest and darkest skin types, overall, evidence supports PI-MED as a protocol for inducing and measuring individual differences in cutaneous inflammation and PI-MED evoked erythema shows potential for expanding psychoneuroimmunology research to better understand immunological and affective processes in the skin. Further, this work adds to a growing body of evidence demonstrating a distinct relationship between inflammation and anhedonia.