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A growing literature indicates that changes in modifiable factors, including diet, can counteract the toxic developmental and reproductive health effects of chemical exposures. In this issue of the Journal , Gaskins et al. (Am J Epidemiol. 2019;000(000):000–000) present data supporting this hypothesis. Specifically, using data on a cohort of 304 women seeking fertility treatment in Boston, Massachusetts, they found that women with higher exposure to ambient air pollutants had lower fertility treatment success but only when they also consumed <800 μg/day of supplemental folate. No association was observed among women consuming ≥800 μg/day of supplemental folate. The public health importance of this interaction is high: Diet and dietary supplement intake are modifiable factors, whereas exposure to air pollution is less so. While this research question is grounded in a strong biological hypothesis related to epigenetic modifications, oxidative stress, and inflammation, this study raises several key questions. In this commentary, we discuss the inconsistency of the interaction across exposure metrics, the possibility of unmeasured confounding by folate intake, and the importance of examining this association in populations with lower folate intake and/or higher exposure to air pollution. [ABSTRACT FROM AUTHOR]