We know wildfire smoke harms your body but that's not all
Charlestown will likely get another dose of smoke from Canadian and western fires this summer
The group had gathered in Paradise, California, at a park that sits on land burned in the 2018 Camp Fire. That wildfire destroyed most of the town and killed 85 people. In the years since, the same region has experienced three other conflagrations that rank among the largest in California history; one joined the Camp Fire as among the deadliest. Within the circle sat Blake Ellis, the program manager of the ecotherapy program associated with California State University, Chico, who invited attendees to lean into their senses and pay attention to the smells, sounds, and feel of the fire.
The ecotherapy program, which is open to the public, offers “place-based, holistic healing practices” and leads guided therapeutic programs in nature, including those focused on rebuilding a relationship with nature and what Ellis calls “good fire.” “The intention is to slow down, relax, engage with your senses, and to be in nature and community with one another,” she added, and to help the brain write over traumas associated with fire and create neural pathways that connect it with more positive experiences. The ultimate aim is to build resilience within a community repeatedly impacted by devastating wildfires.
Over the last decade, wildfires and their smoke have spread into new regions and grown into a more menacing threat due to climate change. And recently, research has increasingly connected wildfire and smoke with worsening mental health outcomes, in part due to cellular changes in the brain. Papers suggest a link between wildfires and emergency room visits for anxiety disorders, increased rates of post-traumatic stress disorder and depression, and suicides in rural areas. More broadly, decades of research has tied air pollution to spikes in suicide attempts, depression, hospitalizations for mental illness, and other neurological conditions such as dementia.
For those who have experienced wildfires, the traumatic imprint they can leave is clear. But scientists still have numerous questions about how the human brain responds to these events, and, today, economists, epidemiologists, and neuroscientists are working to find answers.
The results are particularly salient for people in rural areas or near undeveloped wildlands, like Paradise, where wildfires have always been a part of life but are becoming more intense, frequent, and dangerous due to climate change and other factors, and where smoke tends to be more prevalent. Coupled with the scarcity of mental health providers — and many other medical specialists — recurring wildfires could create a significant additional stress on an already overburdened mental health system.
Much of what scientists know today about air pollution and the brain dates back to the early aughts, when a group of international scientists began looking at the brains of dogs that were living on the streets in Mexico City, then famous for being one of the most polluted cities in the world. The team examined the dogs’ respiratory passages and several parts of their brains and compared them to the brains of dogs from a less polluted area just to the northeast. The scientists found that canines that spent time in more polluted areas had changes to their blood-brain barrier, as well as neural damage.
Lilian Calderón-Garcidueñas, the toxicologist who led the studies, pointed to the likely culprit: small bits of pollution floating in the air, also known as particulate matter. The team found tiny particles inside brain cells, along with other “things that shouldn’t be there at all — titanium, iron, and copper,” she later told KFF Health News .
When people inhale particulate matter, some of it makes its way from the nasal passages into the lungs, where it can travel into the bloodstream and cross the blood-brain barrier. Some evidence suggests that certain particulates can bypass that pathway altogether, traveling straight from the nasal passages into the brain. Once there, particulates activate immune cells, causing inflammation. That reaction — developed to keep the brain safe from foreign objects and substances — can cause its own harm when kicked into high gear; cells become stressed and degenerate or can’t communicate properly. Toxic substances may also directly affect the functioning of certain cells. Studies suggest that deterioration can lead to cognitive decline and impairment, and it’s been linked to anxiety, depression, and PTSD.
Calderón-Garcidueñas, now at the University of Montana, and her collaborators declared dogs a sentinel species for air pollution’s impact on humans, similar to a canary in a coal mine. Their studies kicked off decades of wider examinations of air pollution and associated disease, including stroke and dementia.
By the time behavioral neuroscientist Megan Herting at the University of Southern California’s Keck School of Medicine began examining air pollution more than a decade later, there was general consensus that air quality has a significant impact on not only bodies, but also brains. “At this point, the data is pretty clear,” she said.
These effects can have different implications on different populations. Infants breathe more quickly than adults, and their brains are more vulnerable. Pregnant people can breathe in contaminants and pass that onto a developing fetus. And people in their later decades of life do not rebound as quickly from acute exposure.
Still, uncertainties remain. Herting, whose lab studies how pollutants influence neurodevelopment, cognition, and mental health, points to questions about how timing of exposure in life impacts the brain and whether or not it recovers. These questions are growing ever more complex, in part, because of the changing composition of air pollutants that can create new toxic threats. “We don't know enough about what is in all of these particles, and what you might breathe every day,” she said.
In a 2023 paper in Nature, scientists at Harvard and Stanford put concerning numbers behind that threat: Since 2016, wildfire emissions had already erased about a quarter of the improvements in particulate air pollution known as PM2.5, largely attributable to regulations like the Clean Air Act, realized over decades. The results were even grimmer in Western states.
The findings, according to University of New Mexico toxicologist Matthew Campen, articulated what many scientists working in public health already feared. “We were making great strides,” he said, but “we hit a plateau.”
And though the respiratory or cardiac implications of noxious smoke may appear glaringly obvious, Campen and other scientists studying the brain suspected there were other important effects. “People do not think about it as a neurological or psychiatric risk,” Campen said. But “that's where the data has been emerging.”
Campen studies toxicants and their impact on vascular, cardiac, and respiratory systems. Over the years, his research has targeted ozone, diesel emissions, microplastics, uranium, and other noxious substances that find their way into the environment and then our bodies. Soon after the Camp Fire tore through Paradise, and an unusually active fire season hit closer to home in New Mexico, he set his attention on wildfire smoke.
At the time, information connecting wildfire exposure and mental health was relatively scarce. A 2022 scoping review found just 19 papers focused on the topic since 1990, with most published after 2014. Just one paper used a physiological measure of mental health data. A broader scoping review from 2021 found 60 relevant papers.
Today, data is still limited, but a growing cohort of researchers — focused on cell cultures, animal models, and wider human population studies — have begun asking questions.
In a series of studies beginning in 2020, Campen and his colleagues exposed lab mice to variations of wildfire smoke for hours at a time over a period of several days. They used naturally occurring events — relying on smoke that drifted from fires burning in Arizona and California — as well as controlled environments where lab-generated wood smoke was filtered into sealed chambers. After less than a month of exposure, they observed neuroinflammation, reduction in serotonin, and the accumulation of amyloid-beta proteins — which form the plaques that some scientists believe may be among the causes of Alzheimer’s disease (a hypothesis that’s been challenged) — in the mice’s brains. Interestingly, these problems did not resolve quickly.
That lingering effect, Campen said, stuck around for weeks in healthy mice and much longer in older mice. And even low levels of smoke, which showed minimal impacts to the lungs, affected the brain and mice behavior. To Campen, these are important findings for humans living with smoke, though he cautions more study is needed to draw a direct connection to the same effects in people. “You might not even know that you're depressed or anxious or what have you as a result of exposures that happened three weeks ago,” he said.
More recently, scientists at Lawrence Livermore National Laboratory and the U.S. Environmental Protection Agency have run tests comparing how brain cells react to exposure of eucalyptus wood smoke in an acute period of 24 hours. They, too, found neuroinflammation as well as signs of leakiness in the blood-brain barrier.
Thus far, the research suggests that some of the physiological originators of mental illnesses — such as neuroinflammation and immune activation — can be present in wildfire smoke-exposed brains. This could result in an uptick in anxiety, depression, and PTSD. But the links are still forming. This summer, a group of researchers at Guangxi Medical University in China and the U.S. Environmental Protection Agency published a commentary calling for more research to understand the correlation between smoke and neurological disruption.
“We are still at the very early stages of really having a mechanistic understanding,” said Burcin Ikiz, a neuroscientist who founded the Neuro Climate Working Group, a global collaboration that includes researchers examining how climate change impacts human brains.
Epidemiological studies — which focus more specifically on identifying broader correlative relationships between exposures and health outcomes — are further along, she said. A study published in 2024 showed that certain mental health-related prescriptions, such as mood stabilizers and antidepressants, increased in the six weeks after a large fire among a cohort of more than 7 million Californians living in impacted areas between 2011 and 2018. A group of researchers from Stanford and Harvard Universities published an analysis in 2025 of nearly 90,000 mental health-related emergency department visits that occurred around California’s 2020 wildfire season. They found that exposure to wildfire smoke — identified using a patient’s residential zip code — significantly increased the likelihood of an emergency visit for a mental health reason. (The team controlled for baseline visits and Covid-19 cases, but it’s difficult to know whether the visits were due to the biological effects of the wildfire smoke or the experience of the event itself.)
In a similar study, conducted as part of a student’s Ph.D. thesis, researchers at the University of California, Irvine examined electronic health records gathered at hospitals in parts of Southern California between 2017 and 2020 and mapped them on top of wildfire particulate matter exposure. In 2025, they published an abstract of the results, which showed an increase in depression-associated emergency room visits during periods when wildfire smoke was present. They expect to finalize the paper to be peer-reviewed and published next year.
Disentangling the specific effects of smoke exposure from the traumatic elements of experiencing wildfires is an exceedingly difficult challenge, but it’s important to consider all the ways that wildfires can impact our health, according to researchers undertaking this work. Ultimately, the effects are likely additive. “Focusing on only one pathway risks underestimating the overall mental health burden,” Jun Wu, the principal investigator and advisor on the UCI study, wrote in an email.
The diseases most often associated with air pollution and wildfire exposure — heart disease, cancer, and respiratory diseases — all rank in the top 10 leading causes of death in the U.S. Suicide ranks 11th. Roughly a quarter of the population suffered from some form of mental illness in 2024. Meanwhile, wildfire smoke is growing worse. That’s true particularly in rural areas that were once relatively free of the type of air pollution that has long burdened cities. The people living there may also be less acclimated to it.
For the heart and lungs, research shows a clear impact from smoke exposure. For mental health outcomes, particularly in the long-term, “the signal is real but messier,” Ikiz wrote in an email, in part because of the challenges in disentangling the direct biological effects from the broader disaster context. “Bottom line: we can quantify parts of this now, particularly acute cardiovascular effects and anxiety signals, while uncertainty is greatest for long‑term outcomes like cancer and some long-term mental-health endpoints,” she added. “The debate is less about whether wildfire smoke can affect the brain and more about how strong and clinically meaningful those effects are.”
As research continues, some of the researchers studying the severity of these impacts are now also looking for ways to blunt them. Environmental efforts, like offering services to vulnerable residents or maintaining access to health care, can give certain people an advantage in avoiding impacts. But certain “biological mechanistic resilience factors” may also make individual brains hardier in the face of dangerous environmental factors like extreme heat and air pollution, according to Ikiz.
Overall awareness can help, too. Programs that train new clinicians aren’t moving fast enough to educate them about the health effects of climate change, said Joanna Katzman, director of public health initiatives at UNM’s Project ECHO, a program that provides online training and workshops to doctors on topics such as pain management and opioids. But she has already seen programs like ECHO — which began hosting climate-focused training five years ago —boost familiarity with the risks.
“The clinician who's taking care of them in the emergency room is much more likely to be thinking ‘Is this related to wildfire smoke? Is this related to extreme heat?’” said Katzman.
Campen, too, is engaging directly with clinicians. This year, he attended the American College of Psychiatrists annual meeting for the first time to speak with psychiatrists about his research findings.
“Most neurologists and psychiatrists see much more extreme cases,” he said. “The relatively subtle but broad-reaching impacts of environmental health often don't really rise to the forefront of their experience and their recommendations.”
Ellis, the director at the ecotherapy program outside Paradise, California, remains a bit of an outlier. She has made such themes central to her treatment philosophy. In addition to the program’s workshops, she sees clients privately and the ecotherapy program has provided forest therapy training to medical residents with Healthy Rural California, a nonprofit organization focused on reducing health disparities in rural areas. Fire-focused programs like the one she helped lead in Paradise may also foster a relationship with nature, controlled fires, and their community, which can help people through life and future fire-related tragedies.
While researchers continue interrogating the mechanisms that contribute, Ellis is working on addressing the symptoms for those on the ground. “We need to have some healing.”
This article was originally published on Undark. Read the original article.
