The Hazard index at thirty-seven: New science new insights

The Hazard Index (HI) was developed as a quantitative tool for characterizing noncancer risks from combined exposures. HI, and related approaches, dominate assessments of such risks. Despite this dominance, HI has limitations: the widespread lack of data required to use the tool; the inability to deal with synergy and potentiation; and the inability to quantitatively predict the probability of specific adverse effects. This article provides a review of recent advancements in toxicology and exposure science and their implications for HI. The new find-ings illuminate aspects of the HI and reduce the limitations of using the tool.