The standard 21-day cumulative irritation test was reexamined to determine if it could be abbreviated in order to lessen costs and delays and simplify operations. The relative scores on 150 cosmetic-type products were compared at 14 and 21 days. In more than 90% of products studied, we found that we would have made the same decision regarding the level of irritation and the relative ranking of the products at either 14 or 21 days. This high correlation between scores at 14 or 21 days justifies using a 14-day test for many products and for product development comparisons.
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Richard et al. (1982) studied this question.
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