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

By Naseem S. Miller

August 7, 2023
Quebec wildfire-bushfire
Bushfire outcomes include mental health disorders, COVID-19 complications, death from heart disease, shorter height, and poorer health. (Andre Pichette/EPA via AAP)

From the US to Canada to Greece, bushfires 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 materials, 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 bushfire 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 bushfires in Canada affected air quality in parts of US.

Moreover, wildfires can upend people’s lives, leading to mental stress.

Several studies have established the short-term health effects of bushfire exposure, finding an association with a 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 a 10% increase in 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 bushfire 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 US, which were published between 1987 and 2022. The majority focus on health impacts one to two years after exposure to a bushfire. 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, bushfires 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 bushfire exposure and child mortality and hospitalisation 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 hospitalisation rates two years after bushfire exposure compared with the year before the bushfire occurred. In addition, people with underlying health conditions, such as overweight or obesity, diabetes and heart disease, and lower income had higher rates of hospitalisations than those without underlying health conditions and higher income.

Two studies found that bushfire exposure is associated with shorter height in children, especially when mums were exposed to smoke during pregnancy. One study suggests that may be due to the impact of bushfire smoke on pregnant mums’ 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 bushfire 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 bushfires.

There are several reasons why bushfires 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 bushfires and length of the bushfire 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 bushfire exposure, more scientific evidence is urgently needed to determine long-term impacts of bushfire exposure on human health.”

Bushfires 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 bushfire exposure during 2017 to 2020, the study authors note.

The intensity and frequency of bushfires are increasing in the US and worldwide. According to the National Oceanic and Atmospheric Administration, there were 20 bushfires that caused more than $1 billion in damage between 1980 and 2021 in the US Sixteen of those have occurred since 2000, according to data from the National Interagency Fire Center.

Bushfires are among the Environmental Protection Agency’s climate change indictors, which show the causes and effects of climate change. Bushfires occur naturally and play a role in maintaining the ecosystems in forests and grasslands, but too many bushfires can throw off nature’s balance.

Bushfire season has gotten longer and there are more bushfires 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 bushfires and air quality

This article first appeared on The Journalist’s Resource and is republished here under a Creative Commons license.

READ MORE:

Twenty years after vast bushfires razed Canberra’s suburbs, bushfire science is not the same

About the author
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By Naseem S. Miller

Naseem S. Miller is a journalist for The Journalist’s Resource.

Tags: 2019 bushfires Australian Research Council and the Australian National Health bushfire season bushfire smoke child mortality environmental pollution heart disease Medical Research Council mental stress PM 2.5 post-traumatic stress disorder respiratory diseases shorter height in children smoke exposure wildfires

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