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What You Should Know About Wildfire Smoke Exposure and COVID-19

Volunteer firefighters manage a live burn during a wildfire training course on May 8, 2021 in Brewster, Washington

David Ryder / Getty Images

Key Takeaways

  • Studies link air pollution from wildfire smoke to increased cases of COVID-19.
  • Wildfire smoke can contain particulate matter and other compounds that can damage your lungs and weaken your immune system, making you more susceptible to respiratory infections.
  • Researchers aren’t sure exactly what’s driving the increase in COVID-19 during periods of poor air quality.

Last year, people in the Western United States faced the dual crises of the COVID-19 pandemic and widespread wildfires.

This year, many Americans will face a similar reality. So far, 82 large fires have burned more than 1.6 million acres across 13 states, spewing smoke to places as far as the East Coast. At the same time, the COVID-19 pandemic rages on, especially among the nearly 40% of American adults who are not yet vaccinated.

As it turns out, wildfire smoke can make the body more susceptible to illness, weakening the system and making way for more severe respiratory illness.

Various studies—including a recent one conducted in Reno, Nevada—indicate that periods of extremely poor air quality are associated with significantly higher rates of COVID-19 cases and sometimes hospitalizations.

“Each of these things by themselves are things that we can see a path to improving and mitigating. The problem is we're not getting the opportunity because it's all happening at once. And that can feel overwhelming,” Michael Kleinman, PhD, professor of environmental toxicology and co-director of the Air Pollution Health Effects Laboratory at University of California, Irvine, tells Verywell.

Researchers are working to better understand the connection between wildfire smoke exposure and COVID-19 to help protect against both.

Wildfire Smoke May Increase Susceptibility to COVID-19

Tiny particles called PM 2.5 make wildfire smoke especially hazardous to human health. These particles can be inhaled deep into the lungs, traveling through the blood stream, and damaging vital organs.

The Reno study indicates that the increased PM2.5 from wildfire smoke also exacerbated rates of COVID-19.

In another study, researchers tracked COVID-19 test positivity rates at a large hospital in Reno, Nevada between May and October 2020 and compared the change in case numbers to the change in ambient PM2.5 during that time period. They found that the smoke in Reno at the time drove a 17.7% relative increase in COVID-19 cases there.

The new study adds to a growing body of research linking air quality and the disease across the West. In San Francisco, increased concentrations of PM2.5 were associated with significantly increased cumulative COVID-19 cases, hospitalizations, and deaths. Kleinman’s research team also found that in Orange County, California, which was less directly impacted by wildfire smoke, periods of poor air quality correlated with spikes in COVID-19 infections two weeks later.

An Attack on the Immune System and Lungs

The data aligns with existing research on the correlation between exposure to polluted air, like traffic smog and cigarette smoke, and risks of respiratory illness.

“We know that particulate matter is bad for our respiratory system. It could weaken our immune response and causes inflammation that then makes it more susceptible to infection from COVID-19,” Daniel Kiser, an assistant research assistant at Desert Research Institute and co-author of the Reno study.

Depending on what the wildfire burns, its smoke may contain hundreds of different toxins. When these enter the body in the blood, they may damage the immune system and vital organs, weakening the body’s ability to fight off infections and making it more vulnerable to pathogens like the COVID-19 virus.

Smoke can contain harmful gases and metals like carbon monoxide, nitrogen oxide, and lead. Even vegetation can contain oils and tar that can be harmful when burned, Kleinman says. These additional components can further irritate the lungs and cause a host of severe health issues. 

“Wildfire smoke is not all that different than cigarette smoke—they’re both biomass burning products,” Kleinman says. “And we know how bad cigarette smoke is.”

What This Means For You

If you live in an area that is affected by wildfire smoke, take precautions to protect yourself from prolonged exposure to the pollution. When the air quality is poor, experts recommend wearing a well-fitted mask that is rated N95 or better, staying indoors with the windows and doors closed when possible, and running an air filtration device to purify the air inside. 

Why Wildfire Smoke and COVID-19 May Be Linked

Researchers don’t yet know exactly why exposure to wildfire smoke and an increase in COVID-19 cases are related. Many of the existing studies show a correlation between COVID-19 cases or severity and wildfires smoke exposure, but don’t necessarily establish causation.

“We want to be cautious,” Kiser says. “The evidence is pointing in the same direction so, obviously, there's a good reason to be concerned about the relationship between air pollution and COVID.”

One proposed reason for this link is that the smoke can actually carry viral particles, allowing them to infect more people. Researchers in Italy found evidence of the COVID-19 virus in particulate matter, which can linger in the air for a long time before settling.

Kleinman postulates that when a person infected with COVID-19 expels viral particles, the virus can cling to particulate matter and travel further than they normally would, possibly infecting more people.

Studies in smokers also suggest that particulate matter could even enhance the expression of the ACE2 receptor in human cells, where the COVID-19 virus attaches to when it infects the body.

It’s also entirely possible, Kiser says, that the connection isn’t biological at all.

“It could be something as simple as, there's a lot of wildfire smoke so people are staying indoors for socializing, rather than socializing outdoors,” Kiser says. “It could also be related to human behavior.”

Regardless of what’s driving this relationship, it’s best to avoid exposure to wildfire smoke to protect your lungs and body. Prolonged wildfire smoke exposure is associated with numerous health risks, like lung disease, heart disease, stroke and neurological deficiencies.

“There are already a thousand good reasons to reduce your exposure to wildfire smoke,” Kiser says. “We already know that it's harmful even apart from COVID-19.”

When air quality is particularly poor, health officials recommend staying indoors to protect yourself from prolongued exposure to smoke. As COVID-19 cases surge nationwide, however, it’s important to be mindful of spending time indoors with people who are unvaccinated or otherwise vulnerable to infection.

High-filtration masks, like those rated N95, can limit your exposure to both COVID-19 and wildfire smoke. To reduce the risk of becoming sick with COVID-19, experts say vaccination is the best tool to protect yourself and others.

“People are going to have to either accept vaccination is a lifesaving tool, or they're going to have to take extra precautions,” Kleinman says.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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