From the U.S. to Canada to Greece, wildfires have been wreaking havoc across the globe in recent months, burning land, forests and homes, and killing or displacing wildlife and humans. The smoke can affect people near and far from the fires.
Wildfire smoke is a mix of gases and fine particles from burning trees, plants, buildings, and other material, according to the Centers for Disease Control and Prevention. The smoke contains small pollutants known as particle matter, or PM 2.5, which are 30 times smaller than the diameter of a human hair. These particles can go deep into the lungs and reach the bloodstream.
Exposure to wildfire smoke can irritate the lungs, cause inflammation, alter immune function, and increase susceptibility to respiratory infections, including COVID-19, according to the CDC. In June, the agency issued an advisory to health professionals about the acute signs and symptoms of smoke exposure, as smoke from wildfires in Canada affected air quality in parts of U.S.
Moreover, wildfires can upend people’s lives, leading to mental stress.
Several studies have established the short-term health effects of wildfire exposure, finding an association with higher risk of death and respiratory and cardiovascular complications. A 2022 study, published in Science of the Total Environment, finds the Australian bushfires in 2019 and 2020 were associated with a 6% increase in emergency department visits for respiratory diseases and 10% increase for cardiovascular diseases.
But there’s still a dearth of population-based high-quality evidence on the long-term health effects of wildfires, according to the authors of “Long-term impacts of non-occupational wildfire exposure on human health: A systematic review,” published in Environmental Pollution in March 2023.
The authors review 36 academic studies, mostly from Australia, Canada and the U.S., which were published between 1987 and 2022. The majority focus on health impacts one to two years after exposure to a wildfire. More than half of the studies focus on mental health. The authors note that most of the included studies were from developed countries with limited data.
The analysis finds in the long term, wildfires and wildfire smoke are associated with mental health disorders, including post-traumatic stress disorder, respiratory diseases and COVID-19 complications, death from heart disease and poorer general health.
Among the findings:
There was no significant long-term association between wildfire exposure and child mortality and hospitalization due to respiratory diseases.
One study from Israel found higher hospitalization rates two years after wildfire exposure compared with the year before the wildfire occurred. In addition, people with underlying health conditions, such as overweight or obesity, diabetes and heart disease, and lower income had higher rates of hospitalizations than those without underlying health conditions and higher income.
Two studies found that wildfire exposure is associated with shorter height in children, especially when moms were exposed to the smoke during the pregnancy. One study suggests that may be due to the impact of wildfire smoke on pregnant moms’ respiratory health.
The authors of the systematic review add that current evidence, although limited, suggests people with certain vulnerabilities — including smoking, lower levels of education, obesity, older age, underlying diseases and lower income — might be at higher risk of negative long-term effects of wildfire exposure.
All 21 studies that assessed the association between wildfire exposure and mental health found negative impacts in adults. Those associations include anger problems, possible post-traumatic stress disorder, depression and heavy drinking. Most studies found a higher rate of PTSD symptoms after exposure to wildfires.
There are several reasons why wildfires have long-term impacts on health, the authors of the systematic review explain.
- Direct impact, including long-term injuries, and even death, resulting from burns and inhalation of smoke during the fires.
- Indirect impact via air pollution and mental stress resulting from economic loss, casualties and forced evacuations.
- Damage at the cellular and molecular level. Air pollution, including smoke, might cause DNA damage, decrease the viability of cells and result in cell death. The smoke can also lead to inflammation in the body and the brain.
“The population-based high-quality evidence with quantitative analysis on this topic is still limited,” they write. “Given the long-term projections of increasing frequency of wildfires and length of the wildfire season due to climate change, the anticipated increase in the frequency and acreage burned by prescribed fires, and the increasing aging population that is more vulnerable to suffer from long-term impacts of wildfire exposure, more scientific evidence is urgently needed to determine long-term impacts of wildfire exposure on human health.”
Wildfires and climate change
Compared with 2001 to 2004, nearly 60% of countries experienced an increased number of days that people were exposed to very or extremely high fire risk and 72% of countries had increased human wildfire exposure during 2017 to 2020, the study authors note.
The intensity and frequency of wildfires is increasing in the U.S. and worldwide. According to the National Oceanic and Atmospheric Administration, there were 20 wildfires that caused more than $1 billion in damage between 1980 and 2021 in the U.S. Sixteen of those have occurred since 2000, according to data from the National Interagency Fire Center.
Wildfires are among the Environmental Protection Agency’s climate change indictors, which show the causes and effects of climate change. Wildfires occur naturally and play a role in maintaining the ecosystems in forests and grasslands, but too many wildfires can throw off the nature’s balance.
Wildfire season has gotten longer and there are more wildfires affecting more areas. This increase is due to several factors, including warmer springs, longer dry summers and drier soil and vegetation, according to the EPA.
The study was funded by the Australian Research Council and the Australian National Health and Medical Research Council. The authors declared no competing financial interests.
How to access this study
Environmental Pollution is published by Elsevier, a Dutch publishing company specializing in scientific research. This study is behind Elsevier’s paywall, but there are several ways you can access it, including emailing the senior author, Shanshan Li. We also have a list of academic journals and publishing companies that offer journalists access to their content upon request.
- Preterm birth and term low birth weight associated with wildfire-specific PM2.5: A cohort study in New South Wales, Australia during 2016–2019 Yiwen Zhang, et al. Environment International, April 2023.
- Wildfire smoke and symptoms affecting mental health among adults in the U.S. state of Oregon Maria C. Mirabelli, et al. Preventive Medicine, November 2022.
- Exposure to wildfire-related PM2.5 and site-specific cancer mortality in Brazil from 2010 to 2016: A retrospective study Pei Yu, et al. September 2022, PLOS Medicine.
- Long-term health effects of wildfire exposure: A scoping review Emily Grant and Jennifer D. Runkle. The Journal of Climate Change and Health, May 2022.
- Long-term exposure to wildfires and cancer incidence in Canada: a population-based observational cohort study Jill Korsiak, et al. The Lancet Planetary Health, May 2022.
- Wildfire exposure during pregnancy and the risk of adverse birth outcomes: A systematic review Sana Amjad, et al. Environment International, November 2021.
- Mortality risk attributable to wildfire-related PM2·5 pollution: a global time series study in 749 locations
Gongbo Chen, et al. The Lancet Planetary Health, September 2021.
- Risk and burden of hospital admissions associated with wildfire-related PM2·5 in Brazil, 2000–15: a nationwide time-series study Tingting Ye, et al. The Lancet Planetary Health, September 2021.
- Psychological effects of the 2017 California wildfires on children and youth with disabilities Elizabeth McAdams Ducy and Laura M. Stough. Research in Developmental Disabilities, July 2021.
- Wildfires, Global Climate Change, and Human Health Rongbin Xu, et al. The New England Journal of Medicine, November 2020.
- The health impacts and economic value of wildland fire episodes in the U.S.: 2008–2012 Neal Fann, et al. Science of The Total Environment, January 2018.
Resources to track wildfires and air quality
- The Fire Information for Resource Management System (FIRMS) U.S./Canada shows all active fires in the two countries. FIRMS also provides a map of wildfires around the world.
- The U.S. Environmental Protection Agency’s AirNow shows the level of air quality based in ZIP code, city or state. AirNow also has a fire and smoke map.
- The National Interagency Fire Center provides current data on wildfires in the U.S., including the number of firefighters fighting the fires and the acres burned.
- The CDC has a guide on how people can protect themselves from wildfire smoke.
- The wildfires layer on Google Maps shows active wildfires.
- Several news outlets track wildfires or air quality and smoke from wildfires, including The New York Times and CNN.