It is desirable to use more objective methods than visual scoring for the assessment of skin irritancy reactions. In the present study the blood flow in skin sites exposed to sodium lauryl sulfate (SLS) was recorded by a laser Doppler flowmeter. The irritant was applied to the volar forearm of healthy volunteers in concentrations ranging from 0.001% to 5% under occlusion for 24 h. The test sites were scored visually and the blood flow was recorded at 3 different times: 26 h, 48 h and 72 h after the application of SLS. Approximately 950 recordings were performed and a clear relationship was observed between the applied doses of SLS, the recorded blood flow values and the corresponding scores. In a few cases a deviation from the general trend was observed, implying that the naked eye might be unreliable for the assessment of skin irritancy reactions.

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