Evaluation of a human patch test for the identification and classification of skin irritation potential

Current regulations require that the skin irritation/corrosion potential of new chemicals is assessed in the rabbit Draize test, although there are opportunities to use alternative methods to identify the most aggressive materials. Previously, we have proposed that it is possible to employ a strategy that avoids the use of animals and at the same time delivers a more relevant assessment of skin irritation/corrosion potential. The approach is to identify corrosive materials in vitro and then proceed to human volunteer testing for skin irritation. In this study, the human 4-h patch test, its interpretation, and results with 29 test materials are presented. Using 14 materials not classified as "Irritating to skin" by EU criteria, 13 classified as "Irritating to skin" by suppliers, and 2 as "Corrosive - causes burns", it is demonstrated that, by evaluating these on human skin in vitro and in vivo, a significant proportion are either over-classified or under-classified. In conclusion, we are convinced that by application of the approach described in detail here, it is possible to avoid the use of animals, whilst at the same time obtaining an assessment of skin irritation/corrosion potential that is more relevant to man, and which, if required, may be used directly for classification and labelling of substances and preparations within the European Union.