Guinea pig maximization test for skin sensitisation: the use of fewer test animals.

Current European Community (Annex V) guidelines recommend the use of 20 test animals in the guinea pig maximisation test for skin sensitization. The suitability, for classification and labelling purposes, of reducing the number of test animals has been examined by analysing the results of 40 studies submitted to the Health and Safety Executive, and by the use of a mathematical model. Our results suggest that in most cases an experiment with ten test animals can be used to determine satisfactorily whether a substance should be labelled with the risk phrase "may cause sensitisation by skin contact". However, serious consideration should be given to the need for additional investigation if two or three of the ten test animals show a sensitisation response. The highest non-irritant concentration of a substance should be used at challenge. Clearer guidance in Annex V on evaluating challenge responses would be beneficial.