To improve energy efficiency and reduce greenhouse gas emissions, government agencies called for air-tight buildings. To reduce the transmission of COVID and the impact of pollutants emitted in homes by products ranging from stoves to personal care products, scientists and engineers looked for ways to improve air circulation. As harmful particulate matter from wildfires crosses international borders, we’re reminded yet again that safeguarding air quality for public health is a balancing act that we can’t afford to get wrong. Drs. Tiffany Harris and Jonathan Dorn discuss the challenges—and possible solutions.