A study published in the journal Scientific Reports suggests that using HEPA air purifiers at home for one month may lead to a small but measurable improvement in brain function among adults aged 40 and older. The research, conducted on 119 participants in Somerville, Massachusetts—a city with high levels of traffic-related air pollution—found that those who used HEPA purifiers performed about 12% faster on tests measuring mental flexibility and executive function compared to when they used a sham air purifier, which appeared identical but did not actually clean the air. Participants were randomly assigned to use a HEPA air purifier for one month, then a sham purifier for another month, with a monthlong break in between, or the reverse. The study took into account factors such as how much time participants spent indoors and their perceived stress levels during the tests. This design helped ensure that the observed improvements in cognitive performance were more likely due to the air purifiers rather than other variables. The findings suggest that cleaner indoor air could be a simple way to help protect the brain from the harmful effects of traffic-related pollution. The study also highlights that exposure to air pollution can negatively affect mental function even after just a few hours. People living near major sources of air pollution, such as highways, are at higher risk. These risks are not experienced equally across the population, with people of color and low-income individuals more likely to live near highways or in areas with heavy traffic. The study did not specifically explore the benefits for older adults, as fewer than 10 participants were over the age of 60. Additionally, the participants only used HEPA air purifiers for one month, so it is unclear if longer-term use might lead to more sustained or greater improvements in cognitive function. While the exact mechanism by which air purifiers improve cognition is still unknown, some research suggests that exposure to fine particulate matter may damage the brain’s white matter, which is essential for communication between brain cells and regions. The brain areas most affected by air pollution—those responsible for mental flexibility and executive function—were the same areas where improvements were observed in the study.