Assessing the default assumption that children are always at risk

This paper establishes that non-elderly healthy adult animal models commonl y display greater susceptibility than young animals to both acute and a wid e range of chronic toxic effects from agents representing numerous chemical classes, including pharmaceutical agents and agents typically regulated as environmental/occupational pollutants. While the general belief that the y oung are likely to be at enhanced risk compared to adults remains the predo minant perspective, the not-infrequent occurrence of greater susceptibility in adults raises questions about the utility of a generic default uncertai nty factor (UF) for the young and suggests consideration of categorical UFs .