Ultraviolet radiation-induced inflammation as a model for cutaneous hyperalgesia

The effects of UVA-I and solar simulated radiation on skin sensitivity to thermal and mechanical stimuli were compared in normal volunteers. Individual minimal erythema doses (MED) for each source were determined and previously unexposed buttock skin was exposed to 1, 2 and 3 MED of each spectrum. Erythema, and mechanical and thermal pain thresholds were quantified from 3 to 72 hours post-irradiation. Irradiated skin did not exhibit pain but hyperalgesia and allodynia were provoked by the applied stimuli after exposure to 2 or 3 MED. There were highly significant decreases in thresholds for both stimuli in exposed skin compared with non-exposed skin. These changes began within a few hours of irradiation, peaked about 24 hours later and persisted throughout the test period. The sensitivity changes broadly followed the erythema response and did not extend beyond the irradiated area. There were only minor differences between the two spectra at comparable erythemal doses. These data demonstrate the usefulness of UVR-induced inflammation as a model of cutaneous hypersensitivity. This model has clinical relevance for the study of hyperalgesia in general and the abnormal sensitivity of sunburnt skin in particular. It is likely to be useful in the assessment of peripherally acting analgesic drugs.