On his way out the door, President Trump has handed fossil fuel industries and other polluters an enormous gift. After years of wrangling, the EPA’s so-called “secret science” rule went into effect on January 6, 2021. The rule mandates that scientists make public all data used for studies that become the basis for environmental regulations. Sounds innocuous enough. But the impact of the rule may make it impossible to do serious epidemiological research and could severely hamper the EPA’s ability to regulate pollutants. Gabriel Filippelli is the Director of the Center for Urban Health and Professor of Earth Sciences at Indiana University-Purdue University Indianapolis.