Barlow, A., B. Drewitt, P. S. Williamson, and J. P. McPherson. Comparison of the 3T3 Neutral Red Uptake Assay and a Three-Application Patch Test in Assessing the Dermal Irritation of a Selection of Personal Care Products. ATLA 1999. 27: 342.

As the quest to develop useful in vitro test methodologies to replace rabbit eye and skin irritation tests continues, validation projects still depend on historical rabbit eye and skin irritation data as the benchmark against which to measure the performance of the in vitro assays. During our daily contact with sponsors, we are asked more and more about the relationship between in vitro test methods and the results of human trials, especially in the area of skin irritancy. To date, there is a limited amount of data available in the literature which compare the results of in vitro methodologies with those of human volunteer trials. In this study, data obtained in a simple cytotoxicity assay, the 3T3 neutral red uptake (3T3 NRU) assay, will be compared with data from a standard three-application patch test. A selection of 20 personal care and cosmetic products will be tested in a single-blind, within-subject comparison three-application patch tests on a panel of 30 healthy human volunteers. Skin irritation potential will be determined by assessing and scoring the volunteers’ reactions to the products. Products will be ranked according to their irritancy potential in vivo and in vitro, and the relationship between each of the EC values of the NRU assay and patch test results will be determined.