Pain and thermal burns in skin areas previously exposed to ultraviolet radiation

¹ U.S. Naval Air Development Center, Aviation Medical Acceleration Laboratory, Johnsville, Pennsylvania

In order to evaluate the relationship of tissue damage to pain sensation in areas of hyperalgesia, the skin of three subjects was irradiated with injurious doses of ultraviolet radiation and then exposed to thermal radiation. Measurements were made of the pain-threshold-lowering effect of the ultraviolet radiation and, following the development of the hyperalgesia, of the lowering of the blister threshold to thermal radiation. Lowering of the pain threshold of 4–7°C was observed, while the lowering of the blister threshold (i.e. the temperature at which blistering was produced) was of the order of 0.5°C. The ultraviolet-irradiated hyperalgesic skin is therefore not more fragile as regards moderately high temperature (50°C) and high temperature burns than is normal undamaged skin. This finding is in keeping with the previously proposed theory that the intensity of pain is a function of the relative reaction rates at the thermal threshold and at skin temperatures above this threshold. Theory predicts, however, that ultraviolet-irradiated skin heated to, and maintained at, relatively low temperatures (40–45°C) will be more easily blistered than will undamaged skin.