Smoke from the recent Los Angeles wildfires poses a host of well-known human health risks, particularly to the heart and lungs systems. And as climate change fuels longer wildfire seasons, concerns over smoke exposure and the health threats of fires are growing. But the effects of air pollution on the brain are only beginning to be widely recognized.
In a recent study, researchers found that long-term exposure to fine particulate matter, also known as PM2.5, was linked to an increased risk of dementia. But not all air pollution carries the same risk.
Wildfire smoke appears to be especially hazardous, according to Joan Casey, the study’s lead author, adding that the findings highlight the link between climate change and negative neurological consequences.
“We have this aging population, and we have strengthening climate change, and those may converge for really bad neurological health outcomes,” said Casey, an associate professor of environmental and occupational health sciences at the University of Washington.
The study analyzed the health records of more than 1.2 million Southern California residents who were at least 60 years old and lived in areas routinely exposed to wildfire smoke. Each resident was free of dementia when the study began. Researchers then estimated each person’s exposure to PM2.5 based on three-year air-quality and weather-data averages.
By the end of the study, more than 80,000 residents had been diagnosed with dementia. Older adults who were exposed to higher levels of wildfire PM2.5 had an elevated risk of developing dementia. Non-wildfire PM2.5 exposure only slightly increased the odds of a dementia diagnosis.
Casey’s research is the latest in a growing literature that reveals associations between air pollution and harmful cognitive effects. Previous studies have found that people who inhale higher concentrations of PM2.5 from diesel exhaust or other traffic-related air pollutants are more likely to show signs of Alzheimer’s disease in brain tissue.
The Clean Air Act, enacted in 1970, caused a significant decrease in airborne particulate matter concentrations across the country. But more recently, studies have shown that there was a strong uptick in concentrations in 2016 due to increased wildfires fueled by climate change.
Research published in the Lancet Planetary Health found that air pollution continues to be the world’s largest environmental health threat. Taken together, outdoor and indoor air pollution contributes to nearly 7 million premature deaths annually, according to the World Health Organization. Outdoor air pollution alone accounted for an estimated 4.2 million premature deaths in 2019.
“We’re getting a lot of epidemiological evidence that air pollution, particularly high exposures and chronic exposures, may be bad for the brain and bad for your nerves,” said Daniel Pastula, a neurologist at the University of Colorado school of medicine.
“Anything we can do to reduce the risk of air pollutants, whether from wildfires or anything else, seems to be increasingly important for brain health,” he said. But more research is needed, he said, to determine the exact connection between negative cognitive outcomes and air pollution.
According to Jacques Reis, a neurologist and professor of environmental medicine at the University of Strasbourg, air pollutants – including fine particles, gases and organic compounds – can cause inflammation in the brain as well as neuron and DNA damage.
Reis said that the effects of particulates on the brain take time to manifest but can change people’s behavior. “They will trigger a lot of modification at the cellular level and it’s why this is a risk factor for neurodegenerative disease.”
While the exact time it takes for particulates to impact brain health remains unclear, we do know that the length and dose of exposure, as well as underlying susceptibility can all play a factor, Pastula said.
When fine particulates infiltrate the heart and lungs, they wreak havoc on the cardiovascular and respiratory systems. In more severe cases, exposure is linked to heart attacks and stroke, as well as lung cancer.
Experts say that without legislation and regulations to slow climate change, and reduce exposure to smoke from wildfires and other sources of PM2.5, the dire health effects will continue to mount.
“If nothing else changes then things for our brains are going to get worse because of the increases in pollutant concentrations attributed to these big wildfire events,” said Marianthi-Anna Kioumourtzoglou, a professor of environmental health sciences at Columbia University’s Mailman School of Public Health.
Kioumourtzoglou’s research has found that air pollution, more specifically PM2.5, accelerates the progression of neurological diseases such as ALS, Parkinson’s and Alzheimer’s disease. To her, the links are “undisputed” even if there are “details to be figured out.”
(c) 2025, The Washington Post · Amudalat Ajasa