"It's not just a few days in these extreme events that you need to protect yourself."
"It is also the days when the sky looks OK [while air quality indexes or weather reports warn of the presence of smoke]."
Dr. Kai Chen, associate professor, Yale School of Public Health
The health effects of short-term PM2.5 exposure, and
subsequently smoke, can range from relatively minor (e.g., eye and
respiratory tract irritation) to more serious health effects (e.g.,
exacerbation of asthma and heart failure and premature death). In
addition, there is initial evidence that short-term smoke exposure may
lead to preterm birth (Picciotto et al. 2024) and impact brain function
(i.e., cognitive performance as measured through a brain-training game)
(Cleland et al. 2022). Fine particles are respiratory irritants, and
exposures to high concentrations can lead to persistent coughing,
phlegm, wheezing and difficulty breathing. Exposure to PM2.5
may affect the body’s ability to remove inhaled foreign materials, such
as viruses and bacteria, from the lungs. For example, some studies have
reported an increase in the risk of COVID-19 cases and deaths in
response to wildfire smoke exposure (Zhou et al. 2021; Meo et al. 2021;
Schwarz et al. 2022). Although most healthy people will recover quickly
from smoke exposure, some may experience health effects such as
pulmonary inflammation and transient reductions in lung function (U.S.
EPA 2019).
United States Environment Protection Agency
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| Vancouver skyline Wildfires and smoke have always occurred in British Columbia, but they
are becoming more frequent and severe as the climate changes. Wildfire
smoke is a form of air pollution that can affect your health. BC Centre for Disease Control |
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Evaluation of air pollution from wildfires presents unique challenges,
compared to air pollution from other sources, such as traffic or
industrial point sources, as smoke exposure is seasonal and episodic in
nature (Gould et al., 2023). Also, as the number and size of wildfires
impacting an area are variable and as smoke production from wildfires is
not constant or steady, the concentration of smoke experienced by
populations can vary considerably, and can include high levels of
exposure for short time periods or moderate exposure levels lasting for
several days or longer. Additionally, to evaluate the health effects of
wildfire smoke, it is necessary to distinguish the contribution of
wildfire smoke from that of other sources of air pollution within the
mixture that people are exposed to. To address this, researchers have
employed a variety of methods to assess exposure to wildfire smoke for
use in health studies including use of land-based PM monitors, satellite
imagery, air quality modelling, comparison of fire versus non-fire
periods, proximity to wildfire burn area, and self-reports. In these
studies, the most commonly used surrogates for wildfire smoke exposure
are PM2.5 (particles with a diameter of 2.5 micrometres or less) and PM10
(particles with a diameter of 10 micrometres or less). For the primary
investigations included in the systematic reviews considered here, the
health outcome data were based on administrative sources (for example,
mortality registries, health care utilization data), surveys, or
self-reports. In addition, most of the primary studies focused on
short-term or episodic exposure to wildfire smoke (that is, daily
exposure), while some of the studies assessing mental health impacts
considered health effects in years following the wildfires, and studies
of reproductive or developmental impacts considered wildfire smoke
exposure during the gestational period. It is noted that the health
effects of PM2.5, a key pollutant in wildfire smoke, have
been extensively studied and Health Canada has evaluated the health
risks of ambient PM2.5 (that is, PM2.5 from all sources combined) (Health Canada 2022).
Government of Canada
People who are exposed to smoke from wildfires, according to more recent scientific investigations, are increasingly assailed by lung-damaging toxins, but new discoveries identify that hearts, brains and other body organs are also being damaged by wildfire smoke. Smoke exposure could sound the death knell of up to 1.9 million people in the United States alone, over three decades, according to one 2025 study. Lungs can be penetrated deeply by the concentration of airborne particles known as PM2.5, from wildfires.
PM2.5 is a primary pollutant that air quality indexes measure, but fails to reflect other substances that can be contained in wildfire smoke that include lead, mercury and formaldehyde, cautions Karl Nadeau, dean of the University of California, Los Angeles Fielding School of Public Health. Preliminary research suggests that wildfire smoke may be of greater harm than air pollution from more common sources such as car exhaust. Fire in proximity to urban areas, moreover, may be of particular toxicity, through consuming buildings vehicles and electronics.
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| Smoke and flames from the Palisades Fire fill the sky as seen from the
Pacific Palisades neighborhood of Los Angeles. | Getty Images |
Associations between wildfire smoke and cardiovascular hospitalization, diabetes complications, preterm birth, cancer, impaired cognition and other problems, as well as respiratory effects including attacks of asthma have been associated through scientific analytical studies. Wildfire smoke was linked in a 2024 study to deaths from cardiovascular, digestive, endocrine and kidney diseases. Asthma attacks and heart attacks can increase within an hour, in the presence of the severity of ambient smoke, pointed out professor Michael Brauer with the University of British Columbia.
Cognitive effect research has seen a significant expansion, explains Stephanie Cleland, associate professor at Simon Fraser University in British Columbia. Dr. Cleland was lead author of a 2022 study finding smoke exposure to be associated with lower scores on a 'brain training' game. A link between cumulative exposure throughout a school year and lower standardized test scores was also found through research, while other studies indicate a possible association with dementia.
Less dramatic, lower-level exposures over time have an add-on impact, according to Professor Chen, who suggests the wearing of masks to be avoidance-helpful to exposure to ambient smoke during such events, not necessarily only when the surrounding air is redolent of burning, charred wood, and the atmosphere turns grey in reduced visibility with wildfire smoke. One study published in 2025 linked the risk of death from all causes with three-year exposure to wildfire smoke. Yet another 2025 study concluded that as average wildfire exposure increased, North Americans over age 65 suffered a higher risk of dying from chronic obstructive pulmonary disease.
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| A woman wears an N95 mask to protect herself from high levels of smoke pollution.
Daniiielc, Getty Images
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"The data pretty clearly say that there is no safe level of exposure to
wildfire smoke: the more exposure we get, the worse a range of health
outcomes. The data also pretty clearly show that our notion of sensitive
groups should probably be greatly expanded. In addition to kids,
elderly populations, or anyone else with preexisting conditions, like
asthma, we need to think about populations like pregnant people whose
birth outcomes can be substantially affected by exposure. Portable
indoor filtration is often the best option for many households, and
well-fitting N95 masks can help when outside. "
"Climate change, and in particular increasing fuel aridity brought about
by hotter temperatures and variable rainfall, is playing a central role
in the recent rapid increase in wildfire activity and smoke exposure
throughout the US. It is certainly not the only factor, but is
substantially amplifying the risk brought about by other factors, which
include a century of fire suppression that has left abundant fuels in
our wildlands, as well as increased human construction and activity in
the wildland-urban interface. We can say with strong confidence that
climate change has made these events much more likely and much more
severe."
Marshall Burke, associate professor, Stanford Doerr School of Sustainability
Labels: Asthma, Death, Dementia, Diabetes, Exposure to Dangerous Particulates/Chemicals, Heart, Lungs, Public Health, Smoke Inhalation, Stroke, Wildfires