Skin temperature changes induced by ultraviolet A exposure: implications for the mechanism of erythemogenesis.

Measurement of the change in skin temperature caused by exposure of the skin to ultraviolet (UV) radiation may give insight into the mechanism responsible for the development of the UV erythema. Under controlled environmental conditions we determined the temperature change of skin areas exposed to UVA, up to 24 h after irradiation. The UVA doses given were 3 or 4 times the minimal erythema dose (MED). The 3-MED and the 4-MED doses resulted in elevation of skin temperature. Delayed UVA erythema was accompanied by skin temperature rise, indicating involvement of arteriolar vessels in the UVA erythema. This arteriolar dilation is best explained if we assume that the delayed erythema is caused by a vasoactive mediator, most likely released in the epidermis, which reaches the dermal blood vessels by diffusion. This result, combined with earlier studies, leads to the conclusion that the erythemas elicited by UVA, UVB and UVC are probably all brought about by diffusing mediators, and not by direct action of the radiation on the blood vessels.