A new US study has found that wildfire smoke may be worse for brain health than other types of air pollution and even increase the risk of dementia.

The findings, reported on Monday at the Alzheimer’s Association International Conference in Philadelphia, come as millions spent the weekend under air quality warnings from wildfires spewing smoke across the western US, including a huge wildfire in California that has grown to more than 360,000 acres.

At issue is fine particulate matter or PM 2.5 – tiny particles about 30 times smaller than the diameter of a human hair that can be inhaled deep into the lungs and move to the bloodstream. This pollution – from traffic, factories and fires – can cause or worsen heart and lung diseases, and the new study adds to evidence it may play some role in dementia, too.