Ultraviolet-B induced inflammation of human skin: characterisation and comparison with traditional models of hyperalgesia.

The effect on human skin of over-exposure to solar ultraviolet radiation (UVR) has been well described. The erythema produced is commonly referred to as 'sunburn'. Recently UVR induced inflammation has been utilised as a human model of sub-acute pain. Our aim was to characterise the sensory phenotype of UVB inflammation in human volunteers. We delivered UVB to small areas of volar forearm skin in healthy volunteers and found that the degree of inflammation and concomitant increase in sensitivity to cutaneous stimuli were UVB dose and time dependent. We directly compared UVB induced inflammation and the more established thermal burn and topical capsaicin pain models. UVB inflammation produced precisely demarcated erythematous lesions without secondary flare. Both thermal burns and topical capsaicin produced large areas of flare, indistinguishable in character from the primary lesions. Moreover, UVB inflammation induced large reductions in mechanical pain threshold restricted to the primary lesion site, whereas the more established inflammatory pain models produced not only primary hypersensitivity but also significant areas of secondary mechanical hypersensitivity. Taken together these findings suggest that UVB inflammation, at least using moderate doses produces sensory changes primarily by sensitising peripheral pain processing in the relative absence of alterations in central pain processing.