Not just about lungs: What healthcare pros need to know about the wide-ranging impacts of wildfire smoke

Smoke hanging in the air is becoming all too common in Canadian towns and cities during the summer. Indeed, 2025 appears to be on track to match 2023’s record-setting year for wildfires. But it’s not just respiratory conditions like asthma that should have healthcare professionals concerned. From diabetes and cancer to cognitive decline, brain tumours and neonatal implications, the potential effects are far-reaching. And while awareness in on the rise, gaps in knowledge remain about the long-term systemic effects of increased exposure to this pollution. “The long-term consequences of forest fires are a really important area that needs more research,” said Scott Weichenthal, associate professor in the department of epidemiology, biostatistics, and occupational health at McGill University in Montreal. “This is especially because if you're someone who was born in the last five years your entire development is going to be in a world where this is a regular occurrence, and so for those people, it's probably going to be relevant for long-term health.”The primary pollutants of concern from wildfires are the very small particles or particles less than 2.5 µm in diameter that can penetrate deep into the respiratory system, noted Sarah Henderson, scientific director of environmental health services at the BC Centre for disease control in Vancouver. “The early literature around wildfire smoke was focussed on acute respiratory outcomes, and it is now clear to us the wildfire smoke elicits a stronger, acute respiratory outcome than air pollution from other sources. I estimate that the effects are three to four times higher.”Read: The consequences of air pollution and what you can doHenderson, who has been studying the impacts of forest fire smoke for two decades, said while the wider-range impacts are not fully known, the problem is that the very small particles can translocate across lungs and into the bloodstream. “These particles then have access to every organ in your body, and they are small enough to cross the blood brain barrier. So it affects your lungs but it actually affects your whole body.” While studies have linked wildfire smoke to increased risk of cardiovascular disease and stroke, Henderson suggests those risks may be in line with other forms of air pollution. More interesting and worthy of further study, she believes is the impact on cognitive health.Cognitive function“There’s growing evidence that wildfire smoke exposure has a significant impact on brain health,” she said, citing a cohort study of more than 1.2 million residents of Southern California over three years. “The study demonstrated a much higher risk of dementia associated with wildfire smoke than with regular air pollution.”Another longitudinal study found a spike in fine particulate matter lasting just three hours—common during intense wildfire smoke—was linked to noticeably lower attention scores. The finding, which tested participants with brain games, supports other research showing that inhaling smoke can impair cognitive function, causing mental fog, forgetfulness, and fatigue. “It happens within a matter of hours,” noted Henderson.CancerWeichenthal is part of the the McGill Centre for Climate Change and Health, which is tackling the wide-ranging health impacts of climate change, including how rising temperatures and shifting weather patterns fuel the spread of infectious diseases like Lyme and malaria, and how air pollution and extreme weather contribute to non-communicable conditions such as heart disease, respiratory illness and mental health challenges. Weichenthal recently studied the incidence of cancer related to exposures to wildfires. He and his team conducted a population-based observational cohort study of more than 2 million participants in the 1996 Canadian Census Health and Environment Cohort, followed for cancer incidence and mortality from 1996 to 2015. The study was published in the Lancet and found that exposure was associated with an increased incidence of lung cancer and brain tumours.“That sounds terrible, but we shouldn't really be surprised because forest fires are known to emit a range of chemicals that are known human carcinogens,” he said. “The challenge is that because these events now happen regularly often in the same locations, for those people it's really not just a kind of transient exposure. It's something that contributes to their long-term health risks, so we have to look at exposure reduction.”Read" What docs should know: Why wildfire smoke is a 'different beast' from other air pollutionFetal developmentThe impact of fetal development is an important area of study, said Henderson.Among the mounting evidence that in utero exposure to wildfire smoke has lasting impacts, a B.C. study published in ACS ES&T Air that showed infants who were in utero during the severe 2017 and 2018 wildfire seasons in B.C. had a much higher risk of antibiotic-treated respiratory infections in their first year of life. The study focuses on the critical stages of gestational development for parts of the upper and lower respiratory tract associated with the two most-diagnosed respiratory infections: otitis media (i.e., middle ear infections) and lower respiratory infections.“We consistently see that there are effects, and those effects might last a lifetime. Something might happen to you in there that causes your health to be depreciated for the entirety of your life so that you live with, you know, 70 to 80 years with ill health or poor health than you would've had if it hadn't have been smoky for those two weeks when your mom was pregnant.”DiabetesHenderson points to diabetes as another area of emerging study in its relation to wildfire smoke. A 2024 study published in Diabetes Care showed links between diabetes and wildfire air pollution.“There’s growing evidence of (impact on) endocrine function, so we see people with diabetes, for example, having a hard time getting their insulin balanced when it smoky out,” said Henderson. “I wouldn't be shocked if in five years from now we have strong evidence and association between incident diabetes and wildfire smoke, the way we have pretty good associations for regular air pollution.”Mental healthWildfires have been shown to not only contribute to the stress that leads to mental health issues, but the smoke itself may affect worsening mental health conditions.A study published in JAMA Network Open looked at the 2020 California wildfires and found an association between wildfire-specific fine particulate matter (PM2.5) exposure with mental health–related emergency department (ED) visits. The study, led by researchers at Harvard T.H. Chan School of Public Health, found the increase in mental health–related ED visits particularly for young children, minority racial and ethnic groups, and women.“Wildfire smoke isn’t just a respiratory issue—it affects mental health, too,” said corresponding author Kari Nadeau in a release. “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.”Closing the gaps“The biggest gap a lot of scientists are working to fill right now, myself included, is the relationships with incident disease,” said Henderson. “Do we see the populations exposed to more wildfire smoke have more diabetes, more cardiovascular disease, more asthma, more COPD? We know that smoke exacerbates many of these things in the short term when it's happening, but after the smoke clears, what are the longer-lasting health effects of those exposures?”Next, she said, is asking how the magnitude of exposure manifest in outcomes.“You could have one community that gets a huge dose of smoke in five years and another community that has a moderate amount of smoke every summer for five years. Overall they have the same cumulative exposure to smoke, but how does that temporality play into the risk? And is it different for different outcomes? I can very easily convince myself that a big dose of smoke, especially if there's anthropogenic fuels burning, would be more strongly associated with say lung cancer risk than say smaller amounts of smoke every summer, but that's just me talking. We don’t know yet.”A fine balanceWhen counselling patients, Weichenthal recommends healthcare providers:ensure patients have a means of reducing their exposure by staying indoors ensure patients know where to look for real-time air quality informationtalk to patients about indoor air cleaners, noting that they can be built with easily available, inexpensive materials share guidelines with patients with pre-existing conditions so they have a plan for smoky days or in case of exacerbations/worsening healthAt the same time, he notes that patients need to know that the individual risk of incident disease from wildfire smoke is considered small—it’s a matter of reducing risk, while accepting that living involves risk.Henderson agrees: “There are all kinds of other risks in life and if patients get stressed out about wildfire smoke, that's not good for them either. It's a bit of a fine balance.”Seeking solutionsAwareness among the population may be helping. A new study of Ontario’s 2023 wildfire season suggests that public-health messaging can help reduce asthma-related ER visits during smoke events. Researchers found a spike in emergency visits during the first major smoke episode in June, but not during a second episode later that month. The drop may be due to increased public awareness and protective measures, such as heeding air quality advisories and ensuring medications were on hand, the researchers said. The findings highlight that timely information can help people with asthma protect themselves during wildfire smoke events.But Henderson believes that relying on people to protect themselves is not enough. As she wrote in a recent opinion piece in the CMAJ, top-down strategies, such as regulations to ensure quality of indoor air and legislation to protect outdoor workers, are also needed to protect human health as the climate continues to change.“We don't have control over the exposure over this, but we do have control over the indoor environment. I’ve been studying this for 20 years and we have all the evidence we need that this is going to continue. It’s probably going to be a reality for the rest of our lives, so let's start making the changes that are necessary to address it, through indoor air quality legislation.”

Not just about lungs: What healthcare pros need to know about the wide-ranging impacts of wildfire smoke

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