Inhaling traffic-related fumes may increase heart attack risk for up to six hours afterward, a recent study suggests. Researchers from the London School of Hygiene and Tropical Medicine analyzed nearly 80,000 heart attack cases over three years, finding that pollutants from vehicles upped the short-term chance of heart attack.

The reason? It's possible that particles from pollutants such as nitrogen dioxide and PM10 temporarily thicken blood, making it more likely to clot.