Wildfires aren’t going away. Here’s how smoke can affect your health

Three air pollution experts weigh in on what we can learn from Canada’s ongoing wildfires

photo of a baseball stadium with a cityscape obscured by smoke in the background

In recent weeks, Canadian wildfires sent smoke to much of the northeastern United States. Scientists are still learning about the long-term health effects.

AP Photo/Gene J. Puskar

North America’s summer of smoke may well be a harbinger of what’s to come. As record-breaking wildfires in Canada continue to sweep across the land, smoke has been suffusing the skies for more and more people. Frequent fires like these can mean more smoke inhaled, and over longer periods of time.

What are the health consequences of breathing in this fumy miasma? I asked three experts.

Air pollution exposure scientist Jeffrey Brook’s office at the University of Toronto is roughly 500 kilometers from some of the raging blazes that have engulfed more than 8 million hectares in Canada this year. Even at that distance, the air has been bad, he says, shrouding the city in noxious gasses and tiny particles of burned biomass. “It’s the worst particulate matter air quality I’ve seen in 30 years or more,” Brook says.

When I reach him, he’s on a boat on the eastern end of Lake Ontario. All around, the air is hazy from wildfire smoke; he can just make out the shoreline. Driving there from Toronto, Brook felt like he was moving through a curtain, he says.

Some 800 kilometers south, where atmospheric scientist Katelyn O’Dell works at George Washington University in Washington, D.C., the scene has been less apocalyptic, but it can change abruptly. Some days, you can see and smell smoke in the air, and “the sky doesn’t even look blue,” she says.

From across the continent, at the British Columbia Centre for Disease Control in Vancouver, environmental epidemiologist Sarah Henderson says those smoky scenes look all too familiar. “We’re no strangers to wildfire smoke,” she says. In previous years, the region has seen extreme episodes driven by fires in the Pacific Northwest.

These three scientists have been studying the health effects of wildfire smoke for years. They talked with me about how smoke impacts our health, what questions remain and what researchers might be able to learn from the current fires (SN: 9/18/20). Our conversations have been edited for brevity and clarity.

Why are scientists focusing on wildfire smoke? 

O’Dell: The wildfire season has been expanding, so it’s impacting us more throughout the year. [And] wildfire smoke is different than the typical urban smog that has been studied historically.

[That smog], emissions from traffic and industry, has been decreasing due to successful emissions control policies — and those are projected to continue to decrease. Because those are going down and wildfire smoke is going up, it’s really important for us to study wildfire smoke and its impacts on health.

In the coming days, wildfire smoke may continue to sweep across Canada and the northeastern and midwestern United States. The forecast shown predicts when and where particulate matter 2.5 microns and smaller may occur, with darker colors indicating more air pollution. Credit: BlueSky Canada

How can wildfire smoke affect people’s health?

Henderson: Wildfire smoke is a really complex form of air pollution. And we have decades of research that tells us exposure to air pollution isn’t good for us.

What we know at this point is that when smoke is occurring, there are measurable effects in the population almost immediately (SN: 6/17/22). Respiratory effects, especially for people with preexisting respiratory conditions, such as asthma and COPD [chronic obstructive pulmonary disease], are the first things to happen. We generally see that these people need more of their rescue medications, meaning that their airways are closing up.

The magnitude of that impact in those populations seems to be larger for wildfire smoke than for other types of air pollution. We [also] see small detriments to cognitive performance.

And then [there’s] quite a bit of evidence around impacts to the developing fetus. There’s risk of preterm birth and reductions in birth weight for infants who are exposed in utero.

Brook: People will say, “Oh, it’s natural. It’s campfire smoke, it’s OK.” No, it’s not. [Wildfire smoke] contains some of the same toxicants that we think about all the time as bad ones in air pollution.

What’s in wildfire smoke?

O’Dell: There are multiple pollutants in wildfire smoke that can impact health, but the one that we’re typically most concerned with is the fine particulate matter, or PM 2.5. PM 2.5 is a particle in the air that is less than 2.5 micrometers in diameter.

Henderson: Those [are] particles that can travel deep into the lungs.

O’Dell: Wildfire smoke has a lot of gases in it too. Things like formaldehyde, benzene and sometimes ozone.

Ozone negatively impacts respiratory health (SN: 1/4/21). It’s unclear right now if benzene and formaldehyde are often at [dangerous] levels in smoke plumes, but we do know these pollutants at certain levels can negatively impact health from both short-term and long-term exposure. 

What questions do researchers still have about the health effects of wildfire smoke?

O’Dell: If you have a wave of wildfire smoke multiple times every summer, how does that affect your health in the long term? It’s a very important question [and] an open area of research right now.

Henderson: It’s a slightly more challenging question to address because you might have a population that’s exposed for a couple of weeks, at a really high magnitude for one summer, and then for the next three summers, there’s no smoke and everything’s fine.

That intermittent episodic nature of exposure might mean that [the longer-term effects of wildfire smoke] are quite different from the more steady types of air pollution that affect our air quality, day in and day out.

We’re still learning about what that means. We might be seeing kids, if they are exposed very early in life, [with] a lifelong detriment to their lung function.

Brook: What if you happen to be pregnant and the fetus is at a particularly important part of development? If it’s getting really high [smoke] exposure coupled with stress because the mom’s worried about the high exposure, [could] that alter how certain organs – lungs, brain, heart – develop? We don’t know.

O’Dell: [Another] open question is how the health impacts of fresh smoke differ from old smoke [more than three days old]. There are a few reasons [the impacts] might be different, one being chemical changes in the smoke itself — smoke changes as it travels through the atmosphere. Another major factor is the public’s awareness of smoke. If you live close to where the fire is burning, you’re very aware that there is likely smoke. But [people] farther away, might be less aware and maybe take less action to protect their own health.

What can we learn from the current wildfires?

O’Dell: These fires are impacting a different population than have historically been predominantly studied. A lot of the wildfire and health studies have occurred in the western United States. This event that we’re experiencing right now [will] hopefully allow us to have a greater understanding of how wildfire smoke might impact people in the eastern states.

There are many factors that may lead to a different health response for those out east compared with those out west, including different baseline disease rates or levels of pre-existing conditions, different responses to smoke, level of outdoor activity, et cetera.

Henderson: What we need [are] populations that are resilient to these exposures, populations that know how to take protective measures, and policies that look at how we keep smoke out of the indoor environment to ensure that people are protected when they’re indoors. All of those types of things are going to allow us to be resilient to the smoke exposures in the decades ahead.

What can people do to protect themselves from wildfire smoke?

Henderson: [In our current lifestyle], the vast majority of us spend the vast majority of our time inside. If we are effectively reducing smoke in the indoor environment, we are effectively protecting our health for about 90 percent of the time.

We highly recommend that you have some sort of air cleaning device running in at least one room of the home so that you have kind of a smoke-free haven — especially the bedroom because you’re probably going to be there for at least eight hours of the day.

Then we can look to what happens when you’re outdoors. A well-fitted respirator type mask like an N95 or KN95 will effectively filter the particles of wildfire smoke out and probably some of the gases as well (SN: 2/12/21).

O’Dell:  It’s always a good idea to check the local air quality before you undergo any outdoor activity, and then adjust your behavior accordingly. If you really need to be outside, maybe go for a walk instead of a run, and wear a mask if it’s really bad. And if you’re in an extra-sensitive group — children, the elderly, people with preexisting conditions — you might choose to stay indoors on days that are especially smoky.

At the local government level, it’s good to have plans in place for when there is smoke. Do schools cancel recess? Do we open clean-air shelters for people who aren’t able to have clean air in their homes — or maybe don’t have a home — to protect that vulnerable set of the population?

Brook: A key principle we always follow in environmental protection is to set our policies to protect the most vulnerable. It’s always good to be cautious. If you’re healthy, smoke is a little piece of many things in your life that impact your health. But if you’re compromised, maybe you’ve got a respiratory infection or just had a heart attack or some other condition, smoke could really hinder [your] recovery. 

How worried should we be about wildfire smoke? 

Brook: We should be more worried about climate change. When you look at Canada, we’ve had fire impacts from coast to coast this year. I’ve never seen that. It’s just unprecedented. It’s a wake-up call. Like, hey folks, you’ve been hearing that these things are going to happen. And look, they’re happening sooner, they’re happening faster. Look at your air. This is not just bad luck.

O’Dell: In the western United States and even in parts of Canada, [wildfires] have been increasing over the past several decades due to several factors. In the United States, one [factor is] historical fire suppression tactics, but another [is] anthropogenic climate change (SN: 6/9/23). And those increases in fires, and the smoke that they emit, is expected to continue to increase across the coming century.

Henderson:  There are people who live their daily lives in cities that are about as polluted as some of the cities we’ve seen in eastern North America over the past month. On one hand, humans are quite resilient to air pollution exposure, and on the other hand, air pollution exposure is not good for people. We need to find a balance somewhere in the middle that doesn’t make people feel panicked, [and] makes them feel empowered to make the best possible decisions for themselves in their health.

Meghan Rosen is a staff writer who reports on the life sciences for Science News. She earned a Ph.D. in biochemistry and molecular biology with an emphasis in biotechnology from the University of California, Davis, and later graduated from the science communication program at UC Santa Cruz.

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