Visual grading, a laser Doppler flowmeter, a spectroradiometer, a two-channel erythema meter and a Minolta chroma meter were compared in the measurement of erythemas arising from immediate contact reactions produced either by 250 mM benzoic acid or 10 mM methyl nicotinate in petrolatum in an open application test or by ultraviolet irradiation. A good correlation between visual grading and objectively measured values was found for all the instruments, but the laser Doppler flowmeter gave proportionally lower values for the ultraviolet erythemas than the skin reflectance meters, suggesting that these differ from erythemas induced by benzoic acid or methyl nicotinate. The laser Doppler flowmeter gave less repeatable results than other meters when measuring moderate and pronounced erythemas produced by ultraviolet irradiation. Measuring both the blood flow and the actual erythema may give more information about the reaction than either measurement system alone.

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