Long-term health effects of wildfire smoke on the human body

The short-term dangers of inhaling smoke from any fire are scary enough, but new scientific research reveals that breathing in even small amounts of smoke from a wildfire can have dramatic effects on the body in the long term. As wildfires continue to increase in frequency and severity each year, more people than ever are getting regularly exposed to the deadly byproducts of these disasters.

There’s something of a silver lining, though, in that doctors, researchers, and first responders now have access to more data than ever on how these substances interact with the body over time. With more information comes understanding, and the more we understand a threat, the better we’re able to protect ourselves against it.

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How is wildfire smoke different?

Even before they reach inhabited areas, wildfires aren’t like your average campfire. Understanding how wildfires start and why they spread so fast is the foundation for understanding why their smoke is so much more dangerous than other types of fire. Wildfires have much more oxygen available to them and burn much hotter on average than even the biggest bonfires, reaching temperatures in excess of 2,192 ℉. That’s more than enough to melt cast iron. This translates into much more aggressive chemical reactions, transforming the resins within wood and plant matter into volatile organic compounds. The huge scale of modern megafires also dramatically increases the amount of burn products in the air compared to more localized fires. Just looking at one of the simpler burn products, carbon monoxide, the October 2017 fires in Northern California released approximately 2,040 tonnes of CO per hour. The even more massive Canadian megafires in 2023, which burned an area the size of Florida, released as many carbon emissions in 4 months as the entire country of India did in all of 2022.

Wildfire smoke gets even more dangerous when it reaches inhabited areas. As the fire enters the Wildland-Urban Interface, it starts burning many more fuel types from human-made structures and vehicles. Plastics, paints, electronics, and industrial chemicals all burn differently, injecting their own toxic burn products into the mix. Stanford researchers estimate that wildfire smoke can be 10 times as toxic as regular fossil fuel pollution, which is already a leading cause of cancer and other health problems in itself. 

How Far Can Wildfire Smoke Travel?

First responders and those living near the fire are exposed to the most potent mix of wildfire burn products, but part of what makes wildfire smoke such a unique danger is that prevailing winds can carry toxic ashes thousands of miles from their origin. In September 2020, smoke from wildfires in California was detected halfway around the world in the Netherlands. 

The extent of a particular wildfire’s smoke plume, though, depends on the exact weather conditions at the time. Smoke particles can stay in the air for weeks and reach heights of over 5 miles, where high altitude winds can carry them far enough to cover continents. Air currents can just as easily force the smoke down lower to the ground, where it concentrates in valleys, basins, or other low-lying areas. Of course, weather patterns can also change over the course of a fire, shifting the direction, distance, and relative exposure levels of entire regions.

To look up the air quality in your area, as well as track smoke plumes from current fires in North America, take a look at the EPA’s AirNow Smoke & Fire interactive map. At the time of writing, a series of wildfires in Oklahoma has already burned 300,000 acres, prompting a state of emergency across 3 counties.

Long-Term Effects And Risks Of Wildfire Smoke

Using the latest data from across the US and Canada, researchers are warning the public that no level of smoke exposure is safe, with health risks progressively increasing the more a person breathes in. Smoke can impact much more than the respiratory system, too: each component of wildfire smoke interacts with human health in different ways, which complicates the cause-and-effect determination between a wildfire event and a medical diagnosis years later. 

Quoting As Stanford Woods Institute research scientist Jessica Yu explains,, “[Wildfires] can lead to the release of fine particulate matter, harmful gases, volatile organic compounds, and toxic substances, like benzene and heavy metals. Fine particulate matter from wildfire smoke is particularly dangerous because it can penetrate deep into the lungs and enter the bloodstream, potentially causing damage to multiple body systems, including the cardiovascular and nervous systems.”

According to one estimate, between 2006 and 2020, fine particles from wildfires contributed to 24,100 deaths a year in the lower 48 states. The first to show symptoms following a wildfire smoke exposure are sensitive groups, like children and those with pre-existing conditions. Even long after the original exposure, smoke particles trigger the body’s immune system and inflammatory response, increasing the chance of asthma attacks, heart attacks, stroke, and autoimmune conditions. Long-term studies that have tracked children’s health for 2 to 4 years after a nearby wildfire consistently show reduced lung function, increased need for antibiotics, and more time spent in the hospital.

Can Wildfire Smoke Cause Heart Issues?

Even for otherwise healthy adults, exposure to toxic wildfire burn products is a cause for concern. A recent study published in the European Heart Journal found that the risk of a stroke is increased by 1.3% for every 1 microgram per ㎥ of smoke particles. This is twice as dangerous as non-smoke particles of the same size category and concentration. A similar study from Emory University described fine particulate matter as “the most important environmental risk factor for global mortality,” and linked increased wildfire smoke particles to an estimated 20,000 additional heart failure cases each year.

Researchers are still studying exactly why wildfire smoke particles are so much more dangerous than other fine particles, but the evidence suggests that multiple toxic burn products can stick to the ash particles and hitch a ride on them. The extreme temperatures within a wildfire can also chemically alter compounds, transforming normally benign materials like titanium dioxide into much more reactive nanoparticles. When particles below 2.5 microns in diameter enter the lungs, they flow deep into the breathing passages and penetrate the air sacs. Once in the bloodstream, these small particles get distributed throughout the body, embedding in blood vessel walls where they cause inflammation, oxidative stress, and deliver any of the heavy metals or other toxic byproducts.

Can Wildfire Smoke Exposure Cause Birth Defects And Cognitive Effects?

There’s further evidence that links wildfire smoke exposure to birth complications. Researchers at UC Berkeley and UC San Francisco found that pregnant women exposed to wildfire smoke were more likely to have a preterm birth. The effect was strongest during the second and third trimesters, but any exposure to wildfire smoke had a measurable impact on preterm birth risk.

During the Camp Fire wildfire in 2018, the smoke plume passed over a research center housing rhesus monkeys. The macaque population was at the peak of its breeding season at the time. Offspring that were in gestation at the time the smoke plume passed over the colony exhibited significant deficits in their behavioral and physical development, especially in the endocrine system that governs hormonal balance. This was a rare, direct insight into how toxic burn products can pass from the mother’s bloodstream, through the placental barrier, and impact fetal brain development in a higher-order primate similar to humans. 

Strengthening the evidence of developmental impacts in the womb, another study at UC Davis indicated wildfire smoke exposure during pregnancy may also be tied to an increased risk of human children developing autism, up to a 50% higher risk in some cases. The evidence has led researchers to classify wildfire smoke as a possible teratogen, meaning a substance that interferes with fetal development, leading to disability.

In yet another study involving the EPA, CDC, and University of North Carolina, researchers linked high levels of fine particulate matter, like that released during wildfires, to measurable cognitive effects among adults. For each 1 microgram per ㎥ of long-term fine particle exposure, cognitive scores decreased by 0.1% across all age, gender, and education groups. 

Safeguarding Long-Term Health From Wildfire Smoke

Image source: MIRA Safety®

With the growing body of evidence linking even short-term exposure to long-term complications, protecting the air you breathe from the growing threat of wildfires is more important than ever. Keep an eye on the air quality reports for your area using www.AirNow.gov or your weather app of choice. Even when a wildfire may not be near you, increased fine particulate matter concentrations (listed as PM2.5) can indicate if smoke from a distant fire may be reaching your area.

If the air quality starts to dip, the CDC recommends staying indoors with the windows closed as much as possible, preferably with an HVAC system on and a fresh filter installed. Staying inside 24/7 isn’t practical for most people, though, so if you or your family must step outside, the CDC recommends wearing a well-fitted N95 respirator or better to filter out fine particles from the air. However, N95 respirators won’t filter out gases like ozone, carbon monoxide, or nitrogen oxides, and the closer you are to a fire, the more of these toxic gases will be in the air. Our complete guide to surviving a wildfire covers the full protective playbook, from shelter decisions to evacuation timing to the gear that actually makes a difference.

In order to prepare for all respiratory threats, MIRA Safety® specializes in equipment that provides full respiratory protection for the entire family. Our Fire Escape Pro Kit protects against all respiratory threats present in wildfire smoke, allowing you to escape danger, get to safety, or just go about your day with peace of mind, even when smoke is on the horizon. If evacuation becomes necessary, our wildfire go bag guide walks through exactly what to pack — and what to leave behind — so you're ready to move the moment conditions change.