Abstract
The interaction of background disease processes with environmental induced diseases has long been an issue of considerable interest and debate with respect to its impact on risk assessment. Whether and to what extent these processes should be considered independent or additive to background has been the principal focus of debate. The concept of hormesis, a biphasic dose response characterized by a low dose stimulation and a high dose inhibition, as framed within the context of post-conditioning, reveal the occurrence of a third type of "background" possibility, that of "subtraction to background". This novel application of the hormesis concept, which is framed within the biological context of post-conditioning adaptive processes, offers considerable implications for the assessment of aging and environmental risk assessment.