What is in this smoke? Why is it so toxic?
Yes, breathing wildfire smoke can harm your health – here’s what you can do to protect yourself
Wildfire smoke from fires burning in Canada and northern Minnesota has been pouring across the Great Lakes and northeastern U.S. states, turning skies an eerie shade of orange. In the West, smoke has also been spreading into communities in Colorado and neighboring states as more wildfires burn in hot, dry conditions in July 2026.
University of Colorado environmental health researcher Colleen Reid explains what’s in that smoke and why breathing it is a health concern everyone should be aware of.
What is in wildfire smoke?
Wildfire smoke is a complex mixture that includes nitrogen oxides, volatile organic compounds, polycyclic aromatic hydrocarbons, carbon monoxide, carbon dioxide and particulate matter. When homes or buildings also burn, they can release an even more toxic stew of chemicals from burning electronics, furniture, plastics, paints and much more.
What you see when you see a smoke plume or when the air is hazy with wildfire smoke are the tiny particles that are too small to fall to the ground right away with gravity.
These particles, which scientists call particulate matter, are very small – we measure them in microns. When you breathe them in, they can harm your health. The smaller the particles, the deeper they can get into your lungs and body.
You may have heard the term PM2.5. It means particles that are 2.5 microns or smaller in diameter, many times smaller than the width of a human hair. High concentrations of these particles in the air during wildfire smoke episodes are what trigger air quality alerts.
Has wildfire smoke been increasing recently, and why?
Yes, wildfires have become more frequent and more intense just in the past couple of decades, and when wildfires become more frequent and intense, so does the smoke.
Scientists have found that wildfires are becoming more frequent due to a variety of factors that include increases in fire weather – hot, dry, windy conditions that fuel the spread of fires due to climate change – as well as other natural and human factors. The reasons for the increases in wildfires vary in different parts of the world.
Other studies have found that wildfire smoke makes up an increasing portion of the PM2.5 in the air in the U.S., and in many areas it is offsetting the decreases in air pollution that the U.S. has gained through regulations of industrial and vehicle emissions under the Clean Air Act.
How could wildfire smoke affect my health?
Some effects of breathing wildfire smoke include shortness of breath, coughing, itchy or watery eyes, headaches, rashes and itchiness. But smoke can cause more serious harm. Numerous epidemiological studies have shown that hospitalizations and emergency department visits for asthma and other respiratory diseases increase during wildfire smoke events.
After you breathe in the particles, they cause inflammation and oxidative stress, and they can move into the blood and spread throughout the body, affecting other organ systems.
Breathing wildfire smoke has been associated with higher risk of preterm births and other issues during pregnancy, and potentially cardiovascular problems such as heart attacks and strokes, although the evidence for these effects are more mixed.
The longer-term health effects of wildfire smoke are less clear, but it is a growing area of research.
Where can I learn more about wildfire smoke risks where I live?
The first thing to do to protect yourself from wildfire smoke is to know how bad the smoke is and how long it is going to last.
One great place to get information for where you live on current wildfire smoke is fire.airnow.gov. You can zoom in on the map to where you live and find color-coded circles reflecting data from both U.S. EPA air-quality monitors and PurpleAir sensors that people have put in their homes.
The colors show the level of PM2.5 at that location and suggest the associated health risk.
To find out how wildfire smoke is expected to change over time in North America, you can look at maps from FireSmoke Canada and the U.S. Interagency Wildland Fire Air Quality Response Program.
What can I do to protect myself and my family from wildfire smoke?
First of all, depending on the level of the air quality index where you are, there are different recommendations. When wildfire smoke reaches unhealthy levels, stay indoors as much as possible, with doors and windows shut to keep the wildfire smoke out.
If you have an air cleaner, use it, but check the filter, as filters can fill up quickly. Similarly, check the filter on your home HVAC system and replace it if needed.
If you have to go outside, consider wearing a well-fitting N95, KN95 or KF94 mask. These masks can protect you from inhaling particles in the air around you. Looser masks, such as surgical masks, mostly protect others from what you breathe out instead. They do not have a tight seal around your mouth, and when you breathe in, the air with all of the particles can find its way around the sides of the mask.
Having a tight fit of the mask to your face is important so that when you breathe, the air is going through the mask and capturing the smoke particles rather than letting them into your body where they cause harm.
If your home is leaky and you can see haze inside, consider going to a public space, such as a library or mall, with a good HVAC system. Some municipalities have designated clean air spaces where anyone can go.
Colleen E. Reid, Associate Professor of Geography, University of Colorado Boulder
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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