COMPARISON OF 4, NONINVASIVE, QUANTITATIVE PROBES OF SKIN IRRITATION INDUCED BY SODIUM LAURYL SULFATE

The effect of ionic surfactants on human skin after both acute and chr onic treatments has been extensively studied with non-invasive methods . However, the effect on skin of high concentrations [1-10%] of anioni c surfactant has not been described previously. Our purpose was to inv estigate the effects of high concentrations and to compare the respons iveness Of four non-invasive methods. The irritation experienced by hu man skin in vivo after application of high sodium lauryl sulfate (SLS) concentrations was quantified using four, noninvasive, invasive, bioe ngineering methods: transepidermal water loss (TEWL), as assessed by a n evaporimeter variation of skin thickness determined by ultrasound B- scan, variation of skin colour and dye adsorption performed by a color imeter. Six volunteers were patch tested for a period of 24-hours with 1.00, 2.50, 5.00 and 10.00% SLS solutions and the skin response quant ified. As expected, there was a significant correlation between the de gree of skin irritation as determined by each method and the concentra tion of SLS. The data showed that the most sensitive method for determ ining skin irritation, with the lowest limit of detection of skin irri tation, was TEWL. Ultrasound B-scan was found to be less sensitive tha n TEWL but more sensitive than both inspection of skin colour and dye adsorption. Dye adsorption onto SLS-treated skin was found to be satur able and followed the Langmuir type isotherm suggesting that in common with other anionic surfactants SLS remained adsorbed on the skin for a long time.