Skin temperature of UV-induced erythema correlated to laser Doppler flowmetry and skin reflectance measured redness.

Abstract

The sensitivity of human skin to UV radiation is investigated by visual grading of the resulting erythema reactions 24 h after exposure to a series of increasing UV doses. Visual erythema assessment is, however, subjective and depends on pigmentation and redness of the adjacent un-irradiated skin and can be aided by skin reflectance spectroscopy and laser Doppler blood flow measurements. Erythema is accompanied by a raised skin temperature, and this reaction might be utilised as a simple objective measurement of UV sensitivity. Sixteen patients with cutaneous malignant melanoma, 16 patients with basal cell carcinoma, and 36 healthy people were phototested with simulated sunlight on previously UV un-exposed buttock skin. The resulting erythema reactions were graded visually 20-24 h post-exposure and measured by skin reflectance spectroscopy and laser Doppler flowmetry, and the surface skin temperature was determined in the erythema reactions and in adjacent un-irradiated skin by a contact thermometer. Skin surface temperature in UV-induced erythema reactions was dose dependent, was statistically identical in skin cancer patients and in healthy people, and was age independent. The average temperature increase in barely perceptible erythema was 0.7°C (SD=1.1°C), and in bright red erythema it was 3.5°C (SD=2.0°C). Skin surface temperature increases were correlated to measurements by skin reflectance spectroscopy and by laser Doppler flowmetry. Skin surface temperature changes can be used as a simple objective measurement of UV sensitivity in healthy people and in skin cancer patients and may be particularly useful in heavily pigmented people where visual assessment of erythema is difficult or impossible.