Short-term exposures to extreme heat and air pollution are individually associated with an increased risk for mortality, with an even greater impact seen with co-exposure, according to a study published in the American Journal of Respiratory and Critical Care Medicine. Md Mostafijur Rahman, PhD, and colleagues examined associations for acute co-exposure to extreme heat and ambient fine particulate matter (PM₂.₅) with all-cause, cardiovascular, and respiratory mortality (2014-2019). All cause mortality risk increased 6.1% on extreme maximum temperature-only days and 5% on extreme PM₂.₅-only days versus non-extreme days. On days with exposure to both extreme maximum temperature and PM₂.₅, risk increased 21%. On extreme co-exposure days, the increased risks for cardiovascular and respiratory mortality were 29.9% and 38.0%, respectively, which were more than the sum of individual effects of extreme temperature and PM₂.₅ only. Co-exposure to extreme PM₂.₅ and minimum temperature revealed a similar pattern. For individuals older than 75, the effect estimates were larger.