In 2017, the community of Seeley Lake, Montana, experienced unprecedented levels of exposure to wildfire smoke. The Rice Ridge Fire, which was started by a lightning strike on July 24, 2017, tore through the nearby drought-stricken Lolo National Forest, eventually burning 155,000 acres before it was contained in mid-September.
Christopher T. Migliaccio, PhD, an immunotoxicologist at the University of Montana, assumed that the wildfires would have immediate short-term impacts on the residents of Seeley Lake. But he and his colleagues wanted to know what the long-term impacts might be, particularly since residents were exposed for such an extended period — 49 days in which the average concentration of fine particulate matter (PM2.5) was 220.9 micrograms per one cubic meter of air (ug/m3), including nine days when the level was greater than 250.4 ug/m3. For reference, the U.S. Environmental Protection Agency (EPA) designates any level over 35.4 ug/m3 as “unhealthy for sensitive groups.” Because PM2.5 particles are so small, they can often travel deep into the respiratory tract and even enter the bloodstream.
Residents were screened three times — once during the wildfire event itself, once in 2018, and again in 2019. The results? Not only did residents have decreased lung function, but that impairment persisted for up to two years in some people, which can translate into higher incidence of lung diseases such as asthma and chronic obstructive pulmonary disease (COPD), and also an increase in respiratory infections, dementia, and other illnesses.
“What we’re learning is that there are so many variables with wildfire smoke that affect its chemistry and potential toxicity,” Migliaccio says. Length of exposure, what the fire burns as it churns through forests and towns, the distance the smoke travels, and the size of the particles all impact toxicity and, subsequently, human health.
In recent years, wildfires have become much more widespread — and their impacts felt by millions more around the world. According to a 2022 study by University of Maryland researchers, increasing global temperatures and more prolonged and severe droughts over the last two decades due to climate change has resulted in three million more hectares of tree cover loss annually — an area roughly the size of Belgium — compared to 2001.
And while the 2023 wildfire season in the United States was relatively mild, Canada experienced its worst fire season ever recorded, sending plumes of smoke as far south as Florida and blanketing densely populated regions of the United States, including Chicago, New York, and Washington, D.C., for days.
While researchers are still sorting through the impacts of that event, a growing body of scientific literature details the short- and long-term effects of air pollution, including wildfire events, on human health and the health care system.
“I think it’s intuitively obvious for many of us that if you put so much smoke in the air, asthmatics, people with COPD, and other susceptible people are going to wind up in the hospital,” says Sara Adar, ScD, an epidemiologist with the University of Michigan. “But what is surprising is that these wildfire events might actually be impacting our health over the long term as well,” with systemic effects on the lungs, heart, brain, and other organs.
Air pollution and cardiovascular health
Joel Kaufman, MD, MPH, first became interested in the link between air pollution and heart health after the publication of several landmark studies in the late 1990s showing that an increase in air pollution was associated with increased mortality, and that most of that excess risk appeared to be from cardiovascular, as opposed to respiratory, disease.
At the time, the primary modifiable risk factors for cardiovascular disease were thought to be well-understood: smoking, diabetes, and high blood pressure and cholesterol. “So I was particularly interested in what I perceived to be the underappreciation and understudied-ness of environmental and occupational factors on cardiovascular health,” Kaufman said.
Kaufman subsequently received funding from the National Heart, Lung, and Blood Institute (NHBLI) and U.S. EPA to launch the Multi-Ethnic Study of Atherosclerosis (MESA) and the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air), both of which have resulted in dozens of peer-reviewed articles showing the impact of air pollution on health.
In one seminal article published in The Lancet, Kaufman and his team documented how air pollution works to advance heart disease: Long-term exposure prematurely aged blood vessels in study participants and contributed to a more rapid buildup of calcified plaque in the coronary artery.
“We’re now to a point where it’s understood that air pollution exposure contributes to both the acceleration of the underlying processes that increase your risk for cardiovascular events like heart attack and stroke, but also that the days with elevated air pollution exposures [such as during wildfires] can trigger an event in a person who’s at risk for having an event,” Kaufman explains.
Air pollution and brain health
But the heart and lungs aren’t the only organs impacted by air pollution, particularly wildfire smoke. Adar and her colleagues recently published a study in JAMA Internal Medicine that found that air pollution increases the risk for dementia, and that some sources of pollution — namely wildfires and agriculture — are far more damaging than, say, windblown dust.
“We walked into that study expecting … that it’s going to be the cars, the diesel vehicles, the coal-fired power plants,” Adar says. “What we saw is [that] those things were important, but agriculture and wildfires appeared even more toxic.”
Agriculture uses neurotoxins as pesticides, and wildfires burn through all sorts of materials. “Sometimes they’re limited to beautiful natural settings but sometimes they rip right through gas stations — everything that you would not want to light on fire and breathe in their emissions,” Adar says.
“I always like to remind people that air pollution is quite similar to cigarette smoking,” Adar continues. “So we know it causes inflammation, we know it can damage our blood vessels, and we know it can alter the autonomic balance of the body … There are all sorts of indirect pathways where air pollution causes atherosclerosis and vascular disease, and that then impacts your brain. But we also think there are local impacts to the brain as well. … Some of those particles are small enough, they can get into the bloodstream and they can cross the blood-brain barrier or cross into the brain through the olfactory bulb.”
Air pollution and the skin
Kathyana Santiago Mangual, a dermatology research fellow at Mass General Brigham, was inspired to investigate the impact of wildfire smoke on skin health when her patients began reporting an exacerbation of their skin diseases during the summer of 2023, when smoke from the Canadian wildfires blanketed the East Coast.
“The particulate matter in smoke can trigger an inflammatory response in the skin by activating certain receptors that lead to oxidative stress,” says Santiago Mangual. “This can lead to an immune response that results in impairment of the skin barrier and ultimately to the development and worsening of atopic dermatitis.”
In fact, Santiago Mangual and her colleagues found that between May and September 2023, there was a huge spike in dermatology visits, corresponding with an increase in concentrations of PM2.5 and carbon monoxide. They published their findings in the academic journal Dermatology and Therapy.
Disproportionate impact and a move toward solutions
Unfortunately, many of those who are most impacted by wildfire smoke and other air pollutants are those with limited resources.
“Our paper highlights that air pollution disproportionately affects vulnerable groups, including low-income communities, the elderly, and children,” Santiago Mangual says. “Implementing community-level air filtration solutions in resource-limited areas, such as installing air purifiers in public spaces like community centers and schools, can be a vital step.”
Adar also emphasizes the need for more education for the general public. For instance, on days when air pollution from wildfires or other sources is high, the message should be that children, the elderly, and those with chronic conditions should stay inside. “You wear a mask if you have to be outside. You use your air purifier if you have one. You keep your windows closed,” says Adar.
Implementing regulations aimed at cleaning up the air we breathe also is critical. Kaufman notes that federal regulations have resulted in significant reductions in air pollution over the last 25 years.
And while some of those gains are now threatened by the uptick in wildfires due to climate change, the solution to both is still the reduction in society’s reliance on fossil fuels. “There’s a lot of literature demonstrating that if we make the changes that we need to prevent catastrophic climate change … the reduction in mortality from air pollution health effects will be enormous,” Kaufman says.
“We pay the price now in terms of changing our sources of energy, which is expensive and may seem to have a payoff in the distant future,” Kaufman continues. “But we have a payoff now in terms of the reduction in air pollution and the resulting health impacts.”
