It’s a given that we associate higher exposure to wildfire smoke with decreased lung health. But a new study, for the first time, links breathing in fine particulate air pollution (labelled by public health scientists as PM2.5) to mental health issues as well.
The study published in JAMA Network Open connected increased exposure to wildfire smoke with a spike in visits to emergency departments for mental health conditions.
“Wildfire smoke isn’t just a respiratory issue — it affects mental health, too,” Kari Nadeau, a researcher at the Harvard T.H. Chan School of Public Health and an author of the paper, said in a press release. “Our study suggests that — in addition to the trauma a wildfire can induce — smoke itself may play a direct role in worsening mental health conditions like depression, anxiety, and mood disorders.”
Smoke Affects Mind and Lungs
The study focused on California between July 2020 and December 2020 — a period covering the state’s worst wildfire season on record, up to that date. The researchers analyzed data on wildfire-specific PM2.5 levels and emergency department visits for mental health conditions, by zip code, according to the release.
They essentially linked emergency mental health visits with PM2.5 levels. The data analyzed treatment for mental health conditions including psychoactive substance use disorders, psychotic disorders, mood-affective disorders, depression, and anxiety.
The study recorded 86,588 such visits. The average concentration of PM2.5 particle specific to wildfires during that period was 6.95 micrograms per cubic meter of air (μg/m3). As the particulate concentrations worsened, the number of emergency mental health visits increased, with exposures at or above 10 micrograms per cubic meter of air leading to “substantially increased” emergency mental health visits, according to the press release. The PM2.5 concentration levels reached 11.9 micrograms per cubic meter during peak wildfire months, with a high of 24.9 μg/m3 in September 2020.
Read More: What Was the Deadliest Wildfire in U.S. History?
Estimating Wildfire Smoke Exposure
It’s difficult to estimate how many people each year are exposed to wildfire smoke, because acres burned doesn’t necessarily translate directly to population affected; smoke moves beyond burn boundaries. Estimates range from over 100 million people in the U.S., if you use the most indirect measures of exposure, to about 10 million if the data only includes people directly impacted by wildfires near their homes.
The American Lung Association’s 2024 “State of the Air” report said that about 65 million people were exposed at least once to unhealthy spikes of exposure to the kinds of particles often found in wildfire smoke over the three years of the study. Such exposure is trending up. According to the report, about 131 million Americans breathed in at least one kind of unhealthy air during the study period.
“In the three years covered by this report, individuals in the U.S. experienced the highest number of days when particle pollution reached ‘very unhealthy’ and ‘hazardous’ levels in the 25 years of reporting the ‘State of the Air,’” according to an ALA press release.
Larger Fires, More Health Risks
Although the number of wildfires per year, at around 70,000 per year, hasn’t increased substantially over the past few years (following a period of growth earlier), the area affected is on the rise. In 2024, the U.S. saw an increase of 122 percent in terms of acres burned compared to the 10-year average, according to U.S. Department of Health and Human Services data.
Other studies have already linked the increase in wildfires to physical health concerns, including one that attributes over 11,000 deaths a year to long-term exposure to wildfire pollutants.
“Given the dramatic rise in western [U.S.] wildfires and the tremendous amount of smoke emitted by these events, prolonged smoke exposure is impacting communities both near and distant from the actual wildfires,“ according to a report in the journal Environmental Justice, Health, and Policy.
That trend refers to physical health issues. We now know to monitor wildfire’s effects on mental health as well.
This article is not offering medical advice and should be used for informational purposes only.
Read More: How The National Park Service Is Working To Prevent Wildfires
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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
