The contribution of scientific knowledge to workplace health and safety measures is becoming more and more relevant. To identify hazards, an increasing number of mechanistic markers (of exposure, of effect, of individual susceptibility) are now available. To be effective, prevention measures should take into consideration not just the hazards, but also the risk which may vary among different populations and across individuals exposed to the same hazard. A new, extremely promising class of molecular markers of gene-environment interaction comes from epigenetics research (e.g., DNA methylation, histone modification, mi-RNA). A recent epigenetic epidemiology study in workers exposed to metals and PM in the metal industry disclosed their potential role as predictor of extremely early effects on gene expression regulating inflammation and blood coagulation function. A possible, worrisome development in applying mechanistic knowledge in exposure monitoring and exposed individuals' surveillance is to divert the attention from the control of exposure and put the focus on the screening of susceptible individuals only. This raises ethical, social and legal issues which may ultimately impact throughout the practice of occupational and environmental health.