The cutaneous response to a known irritant has been assessed in human volunteer subjects using both clinical scoring and two non-invasive instrumental methods; erythema measurement using an erythema meter and capillary blood flow using a laser Doppler device. 2. Aqueous solutions (0.5% and 1%) of sodium hydroxide were applied to back skin for 3, 15 and 60 min with assessments immediately after removal and at 1, 24 and 48 hours. 3. Increased erythema was seen with increasing duration of exposure and an increase was also seen at 1 h, 24 h and 48 h after removal of the patch. The results obtained with the erythema meter paralleled the clinical erythema scores. However, the laser Doppler device showed the greatest changes immediately after removal of the patch with subsequent readings showing a gradual decrease. 4. Statistical analysis of the data has been carried out to determine the accuracy and precision of the assessment procedures and to determine the minimum test panel size for detecting irritant reactions. 5. Comparison between back and forearm skin indicated a greater sensitivity to sodium hydroxide on the back. 6. The results of this study define an ethical approach to testing irritant materials in human subjects and provide the basis for the development of a classification system for cutaneous irritants.
