Ultraviolet Radiation on the Skin: A Painful Experience?

Abstract

Excessive exposure of skin to ultraviolet radiation (UVR) has dramatic clinical effects in humans, and it is a significant public health concern. Discomfort and sensory changes caused by skin sunburn are the main common features experienced by many of us, a phenomena triggered by the combination of long and short wavelengths radiation (UVA and UVB, respectively). Although the biological processes underlying UVR exposure are not fully understood, in the last few years many studies have made significant progress in characterizing sunburn at the cellular and molecular levels, making use of both humans and laboratory animal models. Here we review and reason that UVR can be used as an excellent model of sensitization and inflammation for pain research. UVR, particularly UVB, produces a controllable and sterile inflammation that causes a robust dose-dependent hypersensitivity with minimal confounding effects. Importantly, we show that UVR animal models precisely recapitulate the sensory, cellular, and molecular changes observed in human skin, giving it great confidence as a translational model. Furthermore, in this article, we give an overview of the pharmacology underlying UVB inflammation, the latest advances in the field, and potential new targets for inflammatory pain.

Keywords: Inflammation; Pain; Pharmacology; UVB; UVR.

Figure 1

Features of UVB‐induced inflammation. (A) Cutaneous UVB exposure produces dose‐dependent erythema. From left to right patches of skin were exposed to 1, 2, and 3 MED on the volar aspect of the forearm 24 h previously. (B) Time course of UVB‐induced mechanical hyperalgesia in human volunteers. The white line shows sensitivity of a control site, while the red, yellow, and blue lines show changes after 1, 2, and 3 MED exposure, respectively. (C) Erythema in rat paw, 24 h after exposure of 500 mJ/cm². (D) UVB‐induced mechanical hypersensitivity in rats, before and after exposure to 0 (white line), 250 mJ/cm² (red), 500 mJ/cm² (yellow), and 1000 mJ/cm² (blue). These doses are roughly equivalent to 1, 2, and 4 MED.