Environmental (red) and genetic factors (blue) conspire to generate common disease (purple). Over time, environmental stressors (broadly defined, to include unhealthy behaviors as well as toxicants), along with genetic factors (such as metabolites and biomolecular activities), may act cumulatively to produce disease (left). But because disease course may be so variable (right), depending on a multiplicity of diverse factors, it has been impossible to assess the causative nature of many common chronic diseases. The availability of modern post-genomics methodologies now challenges environmental health science to detail disease causation in terms of all factors that fall under the rubrics of “environment” and “genetics.”