Harmonization of thresholds for primary skin irritation from results of human repeated insult patch tests and laboratory animal skin irritation tests.

Classification of a chemical or chemical product as a primary skin irritant using laboratory animal tests has been defined rigorously and codified in Consumer Products Safety Commission (CPSC) regulations. However, no regulatory agency, including the CPSC, has defined a primary skin irritant threshold for human repeat insult patch tests (RIPTs) that are typically conducted on products, such as cosmetics, anticipated to come into direct contact with humans. Further more, the protocols for animal and human tests are significantly different, as are the schemes for grading responses. Consequently, comparing the results of one type of test with those from the other type has proved to be difficult. In this short communication, we propose a procedure to harmonize the results from these two types of skin irritation tests and suggest that a score of "5" in animal tests, considering 24-h results on unabraded skin, is equivalent to a score of "3" in human RIPTs.