The in vitro skin corrosivity test. Development of method using human skin

To meet the EEC regulations for classification, packaging, labelling and transportation, many new substances have to be tested for their potential cutaneous toxicity. At present, this is assessed in an in vivo rabbit dermal test. The in vitro skin corrosivity test has been developed to identify those substances which would cause a corrosive response in an in vivo test, thereby alleviating the need to assess corrosive substances in an in vivo test. The method, which uses ex vivo rat skin, is based on the observation that corrosive substances cause a significant reduction in the electrical resistance of skin. The present study investigated the possibility of using human skin in the in vitro skin corrosivity test to provide a means of direct assessment of effect in humans. 12 substances were assessed in this model. The transcutaneous electrical resistance (TER) following treatment with distilled water is essentially the same as that for untreated skin. Of the six preparations that would be formally classified as corrosive by the EEC, on the basis of a 4-hr rabbit covered patch test, all caused a sharp fall in the TER for each specimen of human skin on which they were tested. On the basis of these data, the TER threshold for determination of potential corrosivity was judged to be 11.0 kohms/disc of skin. For the five preparations which would be classified as irritant or would not require a label, the reduction was usually much less marked. Continuing work in this laboratory is directed towards an assessment of a much wider range of chemicals using the human skin in vitro model, ultimately with a view to its use as a method of detecting those substances which may be corrosive to the skin of humans, leading to their classification and appropriate labelling.