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. Researchers tracked health records from 1.2 million older adults in southern California between 2009 and 2019. They used air quality monitoring and other data to estimate residential exposure to PM 2.5 over three years from wildfire smoke or other causes. The study found the odds of a new dementia diagnosis increased about 21% for every 1 microgram increase in the concentration of wildfire particles. That compared with a 3% increased risk for every 3 microgram jump in non-wildfire particles, concluded researchers from the Universities of Washington and Pennsylvania. It is not clear why there would be a difference. But with wildfires increasing, this needs more study, said the Alzheimer’s Association chief science officer, Maria Carrillo. That’s especially considering that the risk of Alzheimer’s, the most common form of dementia, is higher for lower-income populations who may have a harder time avoiding unhealthy air, she said. Health warnings urge staying indoors when air quality is poor but “there are a lot of people who don’t have the option to stay home or they work outside,” she noted. The study adds to a growing body of research about the adverse impacts of wildfire smoke on human health. A study released in June linked more than 50,000 premature deaths in California to wildfire smoke exposure of the past decade. Other studies have linked exposure to wildfire smoke to increased risks of heart attacks and premature births.