"The guideline says is that if [a substance tests negative], you may be able to conclude that it's not a corrosive using a WoE approach," Stokes says. Information that might be considered in a WoE analysis includes results from in vitro irritation tests for that substance.
But the false negatives from the corrosion tests were never examined when ECVAM validated the skin irritation models. ICCVAM is currently doing that evaluation, and preliminary results show that the irritation tests fail to classify at least two known corrosives even as irritants. Without follow-up in vivo testing, these corrosives could enter consumer products without any hazard labeling.
"We want to make sure that if something is corrosive, it's not slipped through these tests," Stokes says. "The data we have show it's a possibility. That…indicates that we need to better understand the usefulness of these assays. Our goal is to prevent injury and disease. It's important to us to have accurate safety testing methods."
Another issue is that the false positive rate for the in vitro skin irritation approaches 30 percent—a substantial number of substances are identified as irritants when they really are not.
"We don't want to excessively over-label products as hazardous or people would probably start ignoring safety labels," Stokes says.
The bottom line is that in vitro methods help to reduce animal use, but "full replacement is not something science supports at this point," Stokes says. "We're trying…to find ways and approaches that can further reduce uncertainty in those decisions, to reduce the number of circumstances where you might have to use [an animal]. As we take advantage of new advances in science and technology we'll continue to make progress in this area. It's a win–win—we're protecting both public health and animals."