The Upsetting Truth About What Wildfire Smoke Does to Your Body

Much of Canada is ablaze again, with more than 200 active wildfires having consumed roughly 10,000 square miles (26,000 square kilometers) since January, the Canadian Interagency Forest Fire Centre reported Thursday, June 5.

This escalating situation pumped massive amounts of smoke across the Canada-U.S. border, affecting air quality as far south as Florida, according to the National Oceanic and Atmospheric Administration (NOAA). As climate change lengthens and intensifies wildfire season in many regions across the world, understanding the dangers of smoke exposure is increasingly important. A wave of new research paints a complex picture of how wildfire smoke impacts the body, linking it to startling health outcomes that go far beyond the respiratory system.

“There is an urgent need for research to fully understand the health impacts of wildfire smoke to raise awareness among public and health professionals, as well as to support the development of effective regulations to mitigate the impacts,” Yaguang Wei, assistant professor of environmental medicine at Mount Sinai’s Icahn School of Medicine, recently told the Harvard Gazette.

Wei is the lead author of a new study, published in May in the journal Epidemiologywhich found that wildfire smoke can damage the lungs and heart for up to three months after the fire is out. He and his colleagues linked this “medium-term” exposure to increased risks of various cardiorespiratory conditions, including heart disease, stroke, high blood pressure, pneumonia, chronic lung disease, and asthma.

“Even brief exposures from smaller fires that last only a few days can lead to long-lasting health effects,” Wei told the Harvard Gazette.

Infectious fumes

Wildfire smoke is a mixture of gases, air pollutants, water vapor, and fine particulate matter (PM2.5), according to the Environmental Protection Agency (EPA). It contains significant levels of toxic compounds such as polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs), some of which are known carcinogens. Recent studies even suggest that wildfire smoke carries microbial and fungal pathogens.

One such study, published in the Ism Journal in 2021, noted that 80% of microbes found in wildfire smoke samples were still viable. While it’s still unclear how these organisms survive the extremely high temperatures in wildfires, researchers do have an idea of how they get into the smoke in the first place. George Thompson, a professor of medicine at the University of California, Davis, who was not involved in the study, told Gizmodo that wildfires pull pathogens from the surrounding soil and vegetation as they draw in air.

“The good news is, most of those bacteria and fungi really don’t cause infections [in healthy individuals],” Thompson said. “We’re most concerned for our patients whose immune systems have been impacted already,” such as those receiving chemotherapy or recovering from trauma, he added.

A 2023 study, however, found evidence to suggest that wildfire smoke could raise infection risk among the general population. The findings, published in The Lancet, Planetary Healthassociated California wildfires with an 18% to 22% increase in invasive fungal infections such as valley fever. Thompson pointed out that the study was based on large hospital data, which is “a great start,” but further research will need to corroborate this link.

The brain on fire

The most hazardous component of wildfire smoke is not pathogens, but PM2.5. These minuscule particles penetrate deep inside the lungs and wreak havoc on the respiratory system. Previous research has shown that the tiniest, ultrafine particles can pass from the lungs directly into the bloodstream. This can damage blood vessels and trigger harmful inflammation and oxidative stress in various organs, including the brain.

Multiple studies have associated wildfire smoke exposure with incidence of dementia. Last year, research published in JAMA Neurology analyzed health data from more than 1.2 million Southern Californians aged 60 and older, and found a significant link between long-term exposure to wildfire-related PM2.5 and a heightened risk of dementia.

Specifically, every 1 microgram per cubic meter increase in the three-year average of wildfire PM2.5 raised the odds of a dementia diagnosis by 18%. In comparison, the same increase in PM2.5 from non-wildfire sources was linked to only a 1% greater risk of developing dementia.

“I was expecting for us to see an association between wildfire smoke exposure and dementia,” lead author Holly Elser, an epidemiologist and resident physician in neurology at the University of Pennsylvania, told the Los Angeles Times in 2024. “But the fact we see so much stronger of an association for wildfire as compared to non-wildfire smoke exposure was kind of surprising.”

Psychological fallout

Other studies have linked wildfire smoke to adverse psychological outcomes. Research published in JAMA Network Open in April analyzed data on wildfire PM2.5 levels and mental health-related emergency department visits throughout California between July and December 2022—the state’s worst wildfire season on record. The study found that wildfire smoke correlated with a significant spike in mental health emergency department visits for up to seven days post-exposure.

“Our study suggests that—in addition to the trauma a wildfire can induce—smoke itself may play a direct role in worsening mental health conditions like depression, anxiety, and mood disorders,” co-author Kari Nadeau, a physician-scientist at the Harvard T.H. Chan School of Public Health, said in a university statement.

Questions remain

All of this research demonstrates that wildfire smoke is more than just a respiratory hazard. But experts are still in the early stages of unraveling its complex health impacts—particularly in terms of mental health, Angela Yao, a senior scientist with the Environmental Health Services at the B.C. Centre for Disease Control in Canada, told Gizmodo.

Many questions remain unanswered, she said. For example, “How do you disentangle the impact of smoke from the impact of the fire itself?” Future studies will need to investigate these confounding factors. But, “even with the current evidence that we have—it already gives us confidence that we should take a lot of action,” she added.

To protect yourself from the hazards of wildfire smoke, Yao recommended limiting the length and intensity of time spent outdoors. “The harder you breathe, the more smoke you inhale,” she said. If you must go outside, wearing an N95 mask or a P100 can reduce your smoke exposure, according to the EPA.

Keep windows and doors shut to ensure that your indoor air is safe. It’s also important to make sure your home’s HVAC system is running properly, Yao added. If you don’t have one, you can purchase a portable air filter or build your own using a furnace filter and a box fan.

As wildfire season becomes increasingly impactful, taking steps to protect yourself and your family from smoke has never been more critical. Experts still have a long way to go towards fully understanding the risks of wildfire exposure, but one thing is clear—these hazards aren’t going away any time soon.