Smoke from more than 200 wildfires burning across Canada has been turning skies hazy in North American cities far from the flames. 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.

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.

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. Chemists usually 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.

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 also get some irritation in the nose and throat and maybe some inflammation.

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.

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.

...continued