Expert Commentary

Environment, Health

Wildfires have long-term health effects, both direct and indirect, several studies show

A recent systematic review of studies on long-term impacts of wildfires finds they are associated with mental health disorders, COVID-19 complications, death from heart disease, shorter height in children and poorer overall health.

by | | climate change, wildfires
Orange-color photo of people walking across the street at 42nd St. at Grand Central Terminal in New York City.
Smoke from wildfires in Quebec, Canada shrouds New York on Jun 7, 2023. (Marc A. Hermann / Metropolitan Transportation Authority on Flickr.)

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.

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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.

Study findings

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.

Several studies showed an association between wildfire exposure and increased risk of flu rates, asthma in children and different types of cancer.

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.

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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.”

Listen to Naseem Miller’s conversation about wildfires with Diana Mason on the HealthCetera in the Catskills program on WIOX.

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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.

Funding

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.

Additional research

Resources to track wildfires and air quality

About The Author

Naseem Miller is the senior editor for health at The Journalist’s Resource. She joined JR in 2021 after working as a health reporter in local newspapers and national medical trade publications for two decades. Immediately before joining JR, she was a senior health reporter at the Orlando Sentinel, where she was part of the team that was named a 2016 Pulitzer Prize finalist for its coverage of the Pulse nightclub mass shooting.