The identification and classification of skin irritation hazard by a human patch test

Abstract

There exist various regulatory instruments the purpose of which is to ensure that the intrinsic toxic hazards associated with substances and preparations are identified. In the context of identification of skin irritation potential, the method is normally the Draize test. Guidance notes provided by the OECD and the EEC expect that corrosive substances will have been screened out by a variety of methods. Substances or preparations which cause a sufficient degree of skin irritation will be classified as skin irritants. The primary motivation behind the present work was to introduce the concept that it is possible to assess the hazard potential of a substance or preparation to produce skin irritation in a human study. In the example presented here, 20% sodium lauryl sulfate (SLS) has been chosen as the positive control. With the protocol currently devised, occluded patch treatment with 20% SLS for up to 4 hr produces an irritant response in just over half of the panel. An irritant response is taken as a clinically evident and significant increase in erythema, oedema or dryness—a minimum of a+ reaction on the ICDRG scale. At such a level of response with the positive control (both in terms of intensity and in proportion of the panel), it is then possible to judge and/or to determine statistically, whether the test material has produced a level of skin irritation which is similar to, greater, or lower than the positive control. In this way a human patch test protocol can form a fundamental component of a strategy for the replacement of animals in determination of skin irritation and corrosion potential. By use of a careful and progressive protocol and by comparison of test data against a positive control it is both possible and practical to classify substances and preparations in terms of their skin irritation potential using that endpoint in the species of concern, man.