Skin sensitisation: New perspectives and recommendations

Various methodological aspects of skin sensitisation testing have been explored, particularly in the context of animal welfare considerations and reliability and sensitivity of test methods. Recommendations are made for the conduct of current and proposed OECD skin sensitisation tests with respect to appropriate test configurations for the purposes of hazard identification and labelling, and the requirement for positive controls. Specifically, the following aspects of guinea pig sensitisation test methods have been addressed: (1) the number of test and control animals required; (2) the option of using joint positive controls between independent laboratories; (3) the choice of positive control chemicals; (4) the optimal conduct and interpretation of rechallenge; and (5) the requirement for pretreatment with sodium lauryl sulfate. In addition, the use of the murine local lymph node assay (LLNA) has been considered. A number of conclusions have been drawn and recommendations made as follows:  In many instances, particularly with the conduct of the guinea pig maximisation test, it is acceptable to halve the number of test and control animals used.  An optional scheme for the conduct of joint positive control studies within a co-ordinated group of laboratories is appropriate.  Only one positive control chemical (a-hexyl cinnamic aldehyde) is necessary for the routine assessment of assay sensitivity.  The proper conduct and interpretation of rechallenge can provide valuable information and confirmation of results in guinea pig sensitisation tests.  Sodium lauryl sulfate should no longer be used as a pretreatment in the guinea pig maximisation test.  The LLNA is a viable and complete alternative to traditional guinea pig test methods for the purposes of skin sensitisation hazard identification. These recommendations provide the opportunity for both animal welfare benefits and improved hazard identification.