Assessing the Default Assumption That Children Are Always at Risk

This paper establishes that non-elderly healthy adult animal models commonly display greater susceptibility than young animals to both acute and a wide 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 young are likely to be at enhanced risk compared to adults remains the predominant perspective, the not-infrequent occurrence of greater susceptibility in adults raises questions about the utility of a generic default uncertainty factor (UF) for the young and suggests consideration of categorical UFs.