As dozens of wildfires rage across the US and Canada, blackening the skies once again this summer, scientists are revealing even more about how dangerous wildfire smoke is for our health.
Some of the worst fires – including the Durkee fire in Oregon, the Park fire in California and the Jasper fire in Alberta, Canada – have sent smoke billowing for hundreds of miles around them, blanketing cities like Boise and Calgarywith poor-quality air.
Wildfire smoke is known to be toxic to the body, but just how toxic is starting to come into focus as new studies emerge. Just this week, a decade-long study involving more than 1 million people in southern California found that exposure to wildfire smoke significantly increases the risk of being diagnosed with dementia by 21%, versus other types of air pollution such as from motor vehicles or factories.
Another recent study, also conducted in California, attributed more than 50,000 premature deaths to wildfire smoke exposure. Smoky skies have been linked to spikes in hospital admissions and ambulance calls for conditions such as asthma, and for people who have cardiovascular issues, the risk of cardiac arrests rises 70% during days with heavy smoke.
Those are just a few examples of how wildfire smoke is dangerous to health. The more research is done, the more we are learning about how different parts of the human body are impacted, says Dr Lisa Patel, a pediatrician and executive director at the Medical Society Consortium on Climate and Health. “We’ve long been concerned,” she says, “but people don’t fully understand this threat, because it’s a new one.
Patel, who is also a hospital-based pediatrician, points to the research around wildfires and birth outcomes. “We have pretty good evidence now that it increases low birthweight for infants, and then there is emerging evidence that wildfire smoke increases stillbirth as well,” she says. Exposure to wildfire smoke also increases the risk of preterm birth by 3.4%.
Patel points out that fine pollutants have been studied for years, and the regular kind of fossil fuel-created particulate matter pollution still drives 8.1 million deaths worldwide – more than from tobacco.
But wildfire smoke is even worse. Every part of the body is affected by the tiny particles that enter the circulatory system. There is evidence that pollution from wildfires can move through the placenta and impact a developing fetus’s brain, lungs and liver. “It goes everywhere,” says Patel.
“We’ve known for years that there’s something different about wildfire smoke that makes it more toxic,” Patel says, “And now we’re starting to understand it’s not just respiratory, it’s playing out in other parts of our body as well.”
Researchers are still trying to understand exactly why, but wildfire smoke contains a toxic brew of compounds – including volatile organic compounds, aromatic hydrocarbons and heavy metals. That’s partly due to what is burning: when buildings go up in flames, the smoke will include metals, cleaners and many different types of substances – some that are carcinogenic – that become aerosolized. “All of these things make it worse for our bodies than the fossil fuel pollution that we’re always breathing,” Patel says.
In addition to pregnant people, chronically ill people and the elderly, young children are particularly vulnerable, because their lungs are developing rapidly in the first five years of life, and pound for pound, they are breathing in more smoke than a full-grown adult. A 2021 study estimated that the same level of smoke from wildfires was 10 times more harmful for children’s respiratory health than air pollution from other sources.
How to stay safe
So, given an alarming body of evidence, what’s the best way to stay safe? Patel, who lives in California, says she watches the air-quality index websiteevery day and advises others to make it a habit. She also advises to invest in air purifiers in the home – especially for rooms where you sleep. If you can’t afford one, you can make a DIY version using a box fan and a high-quality filter. Those boxes can reduce air pollution inside the home by 50%-60%.
And if you need to go outside on days with high levels of wildfire smoke, wearing an N95 mask is the best protection, Patel says. “But as we know, the protection is only as good as the fit and only as good as the users willing to wear it. And definitely don’t wear an N95 and go out jogging,” she adds. “The N95 is just meant to keep you safe, but you should still not treat it like a normal day.”
Ultimately, she says, people need to think of these smoky days differently. “We need a new consciousness about this new era of unnatural disasters we’re living in,” says Patel, who is also a member of Science Moms, a group of leading climate scientists and moms who encourage moms to treat the climate crisis like a parenting issue.
“Wildfire days are going to happen again and again. And so we need to change our frame, from thinking that this is going to be a one-off, to understanding that for our kids, it’s more or less going to be the equivalent of a chronic exposure.”
In The Conversation
Smoke from more than 100 wildfires burning across Canada has been rolling into North American cities far from the flames. New York City, Denver, Chicago, Minneapolis and Detroit each made the list of the most polluted cities in the world at times in May and June 2023 because of the fires. The smoke has triggered air quality alerts in several states.
We asked Chris Migliaccio, a toxicologist at the University of Montana who studies the impact of wildfire smoke on human health, about the health risks people can face when smoke blows in from distant wildfires.
What’s in wildfire smoke that’s a problem?
When we talk about air quality, we often talk about PM2.5. That’s particulate matter 2.5 microns or smaller – small enough that it can travel deep into the lungs.
Exposure to PM2.5 from smoke or other air pollution, such as vehicle emissions, can exacerbate health conditions like asthma and reduce lung function in ways that can worsen existing respiratory problems and even heart disease.
But the term PM2.5 only tells you about size, not composition – what is burning can make a significant difference in the chemistry.
Smoke from wildfires in Canada was detected across a large part of the U.S. on June 28, 2023. Dark purple dots indicate hazardous air quality. Light purple indicates very unhealthy air; red is unhealthy; orange is unhealthy for sensitive groups; and yellow indicates moderate risk. AirNow.gov. AirNow.gov
In the northern Rockies, where I live, most fires are fueled by vegetation, but not all vegetation is the same. If the fire is in the wildland urban interface, manufactured fuels from homes and vehicles may also be burning, and that’s going to create its own toxic chemistry, as well. Chemists often talk about volatile organic compounds, (VOCs), carbon monoxide and PAHs, or polycyclic aromatic hydrocarbons produced when biomass and other matter burns having the potential to harm human health.
How does inhaling wildfire smoke harm human health?
If you have ever been around a campfire and got a blast of smoke in your face, you probably had some irritation. With exposure to wildfire smoke, you might get some irritation in the nose and throat and maybe some inflammation. If you’re healthy, your body for the most part will be able to handle it.
As with a lot of things, the dose makes the poison – almost anything can be harmful at a certain dose.
Generally, cells in the lungs called alveolar macrophages will pick up the particulates and clear them out – at reasonable doses. It’s when the system gets overwhelmed that you can have a problem.
Where macrophages are found in alveoli, the tiny air sacs in the lungs.
One concern is that smoke can suppress macrophage function, altering it enough that you become more susceptible to respiratory infection. A colleague who looked at lag time in the effect of wildfire smoke exposure found an increase in influenza cases after a bad fire season. Studies in developing countries have also found increases in respiratory infections with people who are cooking on open fires in homes.
The stress of an inflammatory response can also exacerbate existing health problems. Being exposed to wood smoke won’t independently cause someone to have a heart attack, but if they have underlying risk factors, such as significant plaque buildup, the added stress can increase the risk.
Researchers are also studying potential effects on the brain and nervous systemfrom inhaled particulate matter.
When smoke blows over long distances, does its toxicity change?
We know that the chemistry of wildfire smoke changes. The longer it’s in the atmosphere, the more the chemistry will be altered by ultraviolet light, but we still have a lot to learn.
Researchers have found that there seems to be a higher level of oxidation, so oxidants and free radicals are being generated the longer smoke is in the air. The specific health effects aren’t yet clear, but there’s some indication that more exposure leads to greater health effects.
The supposition is that more free radicals are generated the longer smoke is exposed to UV light, so there’s a greater potential for health harm. A lot of that, again, comes down to dose.
Chances are, if you’re a healthy individual, going for a bike ride or a hike in light haze won’t be a big deal, and your body will be able to recover.
If you’re doing that every day for a month in wildfire smoke, however, that raises more concerns. I’ve worked on studies with residents at Seeley Lake in Montana who were exposed to hazardous levels of PM2.5 from wildfire smoke for 49 days in 2017. We found a decrease in lung function a year later. No one was on oxygen, but there was a significant drop.
This is a relatively new area of research, and there’s still a lot we’re learning, especially with the increase in wildfire activity as the planet warms.
What precautions can people take to reduce their risk from wildfire smoke?
If there is smoke in the air, you want to decrease your exposure.
Can you completely avoid the smoke? Not unless you’re in a hermetically sealed home. The PM levels aren’t much different indoors and out unless you have a really good HVAC system, such as those with MERV 15 or better filters. But going inside decreases your activity, so your breathing rate is slower and the amount of smoke you’re inhaling is likely lower.
A satellite captures wildfire smoke on May 16, 2023. NASA EarthData
We also tend to advise people that if you’re in a susceptible group, such as those with asthma, create a safe space at home and in the office with a high-level stand-alone air filtration system to create a space with cleaner air.
Some masks can help. It doesn’t hurt to have a high-quality N95 mask. Just wearing a cloth mask won’t do much, though.
Most states have air quality monitors that can give you a sense of how bad the air quality is, so check those sites and act accordingly.
