The skin corrosivity test in vitro. Results of an inter-laboratory trial

The collaborative study reported here was performed to evaluate the reliability of the skin corrosivity test in vitro when performed in independent laboratories. Twenty substances were examined in each of three participating laboratories and the results were compared with existing data from standard assays in vivo. The skin corrosivity test is based on the assumption that corrosive substances destroy the skin's natural outer protective barrier, the stratum corneum. Corrosive action in vitro is measured by a fall in the transcutaneous electrical resistance (TER) below a predetermined threshold. A refined test using a MgSO(4) electrolyte solution for TER measurements has recently been shown to reduce the number of false positive results in the test, while maintaining excellent predictive value for skin corrosive substances. Although in the present study there was some variation between laboratories in terms of the absolute mean TER values obtained, all 6 substances corrosive in vivo were correctly predicted by the three laboratories. The other 14 substances ranged from being non-irritant to severe skin irritants in vivo, but the test was unable to discriminate between these different categories in any of the three laboratories. However, these inter-laboratory comparisons demonstrate that the refined skin corrosivity test is a robust and reliable method in vitro for identifying potential skin corrosive substances.