Interlaboratory evaluation of a human patch test for the identification of skin irritation potential/hazard

The human 4 hr patch test provides an opportunity to identify substances with significant skin irritation potential without recourse to the use of animals. To demonstrate the validity of the method it must be relevant and reliable. It is self-evident that the method is relevant to the identification of skin irritation hazards to humans. However, it is essential that the results be reproducible. This paper presents data on a number of substances tested by different laboratories. Eight substances were tested by two or more laboratories and the data compared with a standard positive control, 20% sodium dodecyl sulfate. In almost all cases, the outcome of this comparison was identical. Thus, despite the fact that there is known variability among human subjects in terms of skin reactivity to irritants, this simple method showed good reproducibility for the classification of acute skin irritation potential. Therefore, it is argued that this human 4-hr patch test is a valid alternative to the equivalent rabbit test for the assessment of skin irritation hazard to humans.