Vast areas of Canada are once again battling severe wildfires, with over 200 active blazes scorching approximately 10,000 square miles (26,000 square kilometers) since January, as reported by the Canadian Interagency Forest Fire Centre on Thursday, June 5. This escalating crisis has sent enormous plumes of smoke across the Canada-U.S. border, impacting air quality as far south as Florida, according to the National Oceanic and Atmospheric Administration (NOAA). As climate change extends and intensifies wildfire seasons globally, understanding the diverse health effects of wildfire smoke is increasingly critical. A surge of new research reveals a complex picture of how wildfire smoke impacts the human body, linking it to alarming health outcomes that extend well 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 stated to the Harvard Gazette.
Beyond the Blaze: Lasting Cardiorespiratory Damage
Dr. Wei is the lead author of a recent study published in May in the journal Epidemiology. The research found that wildfire smoke can inflict damage on the lungs and heart for up to three months after a fire has been extinguished. He and his colleagues connected this “medium-term” exposure to heightened 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 emphasized in his interview with the Harvard Gazette.
More Than Just Ash: The Toxic Cocktail and Infectious Agents in Smoke
Wildfire smoke is a complex mixture of gases, air pollutants, water vapor, and fine particulate matter (PM2.5), as defined by the Environmental Protection Agency (EPA). It carries significant concentrations of toxic compounds like polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs), some of which are known carcinogens. More surprisingly, recent studies suggest that wildfire smoke can also transport microbial and fungal pathogens.
A study published in the ISME Journal in 2021 highlighted that 80% of microbes detected in wildfire smoke samples were still viable. While the mechanisms allowing these organisms to survive the extreme temperatures of wildfires remain unclear, researchers have theories about their origin. George Thompson, a professor of medicine at the University of California, Davis, who was not part of this study, explained to maagx.com that wildfires draw these pathogens from the surrounding soil and vegetation as they pull in air.
Dense grey smoke billowing from a Canadian wildfire in Flin Flon, Manitoba, illustrating the source of hazardous air pollutants and airborne pathogens.
“The good news is, most of those bacteria and fungi really don’t cause infections [in healthy individuals],” Thompson stated. “We’re most concerned for our patients whose immune systems have been impacted already,” such as individuals undergoing chemotherapy or recovering from trauma, he added.
However, a 2023 study published in The Lancet, Planetary Health presented evidence suggesting wildfire smoke could elevate infection risk among the broader population. The findings associated California wildfires with an 18% to 22% increase in invasive fungal infections like valley fever. Thompson noted that while the study was based on extensive hospital data, providing “a great start,” further research is necessary to corroborate this connection.
Wildfire Smoke’s Assault on the Brain
The most hazardous component of wildfire smoke is not necessarily pathogens, but PM2.5. These microscopic particles can penetrate deep into the lungs, causing significant respiratory distress. Previous research has demonstrated that the smallest, ultrafine particles can even pass from the lungs directly into the bloodstream. This translocation can damage blood vessels and trigger detrimental inflammation and oxidative stress in various organs, including the brain.
Multiple studies have now linked wildfire smoke exposure to an increased incidence of dementia. Last year, research featured in JAMA Neurology analyzed health data from over 1.2 million Southern Californians aged 60 and older. It found a significant association between long-term exposure to wildfire-related PM2.5 and a heightened risk of dementia.
Specifically, each 1 microgram per cubic meter increase in the three-year average of wildfire PM2.5 was associated with an 18% higher chance of a dementia diagnosis. In stark contrast, 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.”
The Psychological Toll of Smoky Skies
Other studies have connected 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 across California between July and December 2022—the state’s worst wildfire season on record. This study found that wildfire smoke correlated with a significant increase in mental health emergency department visits for up to seven days following 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, explained in a university statement.
Navigating the Unknowns: The Future of Wildfire Smoke Research
This collective body of research clearly demonstrates that wildfire smoke is far more than a simple respiratory irritant. However, experts acknowledge they are still in the early stages of fully unraveling its complex health impacts, particularly concerning mental health, as Angela Yao, a senior scientist with Environmental Health Services at the B.C. Centre for Disease Control in Canada, conveyed to MaagX.com.
Many questions remain unanswered, Yao said. For instance, “How do you disentangle the impact of smoke from the impact of the fire itself?” Future studies will need to meticulously investigate these confounding factors. Nevertheless, “even with the current evidence that we have—it already gives us confidence that we should take a lot of action,” she added.
Protecting Yourself: Practical Steps Against Wildfire Smoke
To safeguard yourself from the hazards of wildfire smoke, Yao recommended limiting the duration and intensity of time spent outdoors. “The harder you breathe, the more smoke you inhale,” she explained. If venturing outside is unavoidable, wearing an N95 mask or a P100 respirator can reduce smoke exposure, according to the EPA.
Indoors, keep windows and doors closed to maintain safe air quality. It is also crucial to ensure your home’s HVAC system is functioning correctly, Yao advised. If you do not have an HVAC system, consider purchasing a portable air filter or even building your own using a furnace filter and a box fan.
As wildfire seasons become increasingly severe and impactful, taking proactive measures to protect yourself and your family from smoke exposure has never been more vital. While experts continue to investigate and understand the full spectrum of risks associated with wildfire smoke, one certainty remains: these dangers are an escalating concern for public health. Staying informed and taking preventative action are key to mitigating the threat.
