In recent years, science has inked a dotted line from the smoggy phenomenon of air pollution to an increased risk of Alzheimer’s disease. Now, new findings suggest the less-than-savory air may do more than that — it might actually speed up the course of the disease.

Researchers from the Perelman School of Medicine at the University of Pennsylvania examined brain tissue from over 600 people diagnosed with Alzheimer’s.

What they found was striking.

People who had lived just one year in areas with high concentrations of fine particulate matter in the air showed significantly more buildup of amyloid plaques and tau (pronounced TOW) proteins, two biological signatures of Alzheimer’s. Those same individuals also experienced steeper declines in memory, judgment and everyday functioning, including speech difficulty and impaired ability to care for themselves.

The study linked even an increase smaller than what is visible to the naked eye in particulate matter 2.5 to a 19% higher risk of worsened disease. For reference, PM 2.5 is about half as thick as one strand of spider’s web. Common sources of these ultrafine particulates are difficult to avoid, as they include common byproducts of modern life like car exhaust and industrial emissions, as well as natural disasters like wildfires (and their commensurate smoke). They are tiny enough to bypass the lungs and enter the bloodstream, creating a cascade of health concerns.

While earlier research has tied PM 2.5 to dementia and cognitive decline, this study is the first to link it directly to the brain damage seen in Alzheimer’s. It’s a sobering reminder that where we live matters — not just for our lungs, but for our minds.