Comprehensive outlook of in vitro tests for assessing skin irritancy as alternatives to Draize tests.

In vitro alternative methods have been verified for the possibility to assess cutaneous irritancy because humans cannot be direct initial experimental subjects and animal experimentation could be forbidden in the near future. Many kinds of cell cytotoxicity assays have been tried, revealing their own advantages and limitations. Cell function-based tests have been used less frequently than cytotoxicity assays. Three-dimensional culture systems are promising because they are closer to the actual in vivo skin, and some of them are commercialized nowadays. The ultimate objective of in vitro irritancy tests, which is the high degree of correlation with human in vivo test results, has been accomplished in many experimental settings. Before applying these in vitro methods we must consider several points, including cell sources, irritant characteristics, exposure time, endpoint of experiment, extrinsic factors affecting irritation, etc. In vitro skin irritancy tests have been developed continuously, and in the future they could assume a heavy responsibility of estimating the irritancy in human skin in vivo.