Skin temperature and phototest evaluation

The degree of erythema following UV irradiation is known to depend upon skin temperature at the time of UV exposure. We investigated whether changes in skin temperature at the time of erythema assessment influenced the level of erythema. Twenty-two healthy people (mean age 26 years) were irradiated with solar stimulated radiation on previously UV un-exposed buttock skin. The erythematous reactions were evaluated 20-24 h after irradiation by visual scoring and by measurements of skin reflectance and laser Doppler flowmetry. The readings were done at the baseline level at 21 degrees C room temperature where skin temperature was 30.0 +/- 1.7 degrees C and subsequently after skin warming to 37.2 +/- 2.5 degrees C and after cooling to 22.8 +/- 2.6 degrees C. After skin warming, a clinically evaluated erythema grade [0, (+), +, ++, + + +] was scored higher for at least one reaction in 10 of 22 individuals (45%). In the same proportion of subjects, changes to lower erythema grades were detected upon cooling. Skin warming caused an increase in laser Doppler blood flux, but skin cooling did not have a significant effect on cutaneous perfusion. Skin redness measured by skin reflectance was relatively stable during the cooling phase, but a significant increase in skin redness was noted for 0 reaction upon skin warming. For ++ and + + + reactions a small but significance decrease in reflectance was noted. Our results indicate that alterations in skin temperature, especially a temperature increase, modulates the degree of UV-induced erythema moderately. The temperature-dependent changes as an assessment of the (+) reaction are of practical significance, since this reaction is used for the assessment of cutaneous photosensitivity.