Researchers find that wildfire smoke poses neurological hazards

Inhaled microscopic particles from wood smoke can work their way into the bloodstream and reach the brain, putting people at risk for premature aging and various forms of dementia, depression, and even psychosis

Satellite photo, smoke from California fires
Satellite photo, smoke from California fires at 7:01 p.m. PDT Aug 4, 2021.

The research outlined below by the University of New Mexico Health Sciences Center is further evidence of the importance of smoke management. Land managers, agency administrators, and incident management teams need to constantly consider methods of reducing smoke exposure to firefighters and the downwind population when planning, conducting, or suppressing wildfires and prescribed burns.

Woodsmoke from massive wildfires burning in California shrouded much of the West last summer, making it harder for people suffering from respiratory illnesses to breathe.

Those respiratory consequences can be dangerous — even life-threatening — but Matthew Campen, PhD, a professor in The University of New Mexico College of Pharmacy, sees another hazard hidden in the smoke.

In research published online this week in the journal Toxicological Sciences, Campen and his colleagues report that inhaled microscopic particles from woodsmoke work their way into the bloodstream and reach the brain, and may put people at risk for neurological problems ranging from premature aging and various forms of dementia to depression and even psychosis.

“These are fires that are coming through small towns and they’re burning up cars and houses,” Campen says. Microplastics and metallic particles of iron, aluminum and magnesium are lofted into the sky, sometimes traveling thousands of miles.

In the research study conducted last year at Laguna Pueblo, 41 miles west of Albuquerque and roughly 600 miles from the source of wildland fires, Campen and his team found that mice exposed to smoke-laden air for nearly three weeks under closely monitored conditions showed age-related changes in their brain tissue.

The findings highlight the hidden dangers of woodsmoke that might not be dense enough to trigger respiratory symptoms, Campen says.

As smoke rises higher in the atmosphere heavier particles fall out, he says. “It’s only these really small ultra-fine particles that travel a thousand miles to where we are. They’re more dangerous because the small particles get deeper into your lung and your lung has a harder time removing them as a result.”

When the particles burrow into lung tissue, it triggers the release of inflammatory immune molecules into the bloodstream, which carries them into the brain, where they start to degrade the blood-brain barrier, Campen says. That causes the brain’s own immune protection to kick in.

“It looks like there’s a breakdown of the blood-brain barrier that’s mild, but it still triggers a response from the protective cells in the brain — astrocytes and microglia — to sheathe it off and protect the rest of the brain from the factors in the blood,” he says.

“Normally the microglia are supposed to be doing other things, like helping with learning and memory,” Campen adds. The researchers found neurons showed metabolic changes suggesting that wildfire smoke exposure may add to the burden of aging-related impairments.

The research team included colleagues from the College of Pharmacy and the UNM Departments of Neurosciences, Geography & Environmental Studies, and Earth and Planetary Sciences, as well as researchers at Arizona State University, Michigan State University and Virginia Commonwealth University.

Story provided by University of New Mexico Health Sciences Center. Original written by Michael Haederle.

Journal Reference:

David Scieszka, Russell Hunter, Jessica Begay, Marsha Bitsui, Yan Lin, Joseph Galewsky, Masako Morishita, Zachary Klaver, James Wagner, Jack R Harkema, Guy Herbert, Selita Lucas, Charlotte McVeigh, Alicia Bolt, Barry Bleske, Christopher G Canal, Ekaterina Mostovenko, Andrew K Ottens, Haiwei Gu, Matthew J Campen, Shahani Noor. Neuroinflammatory and neurometabolomic consequences from inhaled wildfire smoke-derived particulate matter in the Western United States. Toxicological Sciences, 2021; DOI: 10.1093/toxsci/kfab147

Thanks and a tip of the hat go out to Gerald.

A brief look — wildland firefighter smoke exposure and risk of lung and cardiovascular disease

Wildland firefighters and smoke

Here is a very brief look at the effects of smoke on wildland firefighters, and below that, a longer look, in the embedded four-page .pdf document.

By Kathleen M. Navarro, U.S. Forest Service
(currently with the Centers for Disease Control and Prevention)

Wildland firefighters are exposed to health hazards including inhaling hazardous pollutants from the combustion of live and dead vegetation (smoke), and breathing in  ash and soil dust, while working long shifts with no respiratory protection. This research brief summarizes a study estimating long-term health impacts of smoke exposure for wildland firefighters (Navarro et al. 2019). The study estimated relative risk of lung cancer and cardiovascular disease mortality from existing particulate matter (PM) exposure-response relationships using a measured PM concentration from smoke and breathing rates from previous wildland firefighter studies across different exposure scenarios.

Key Findings:

  • Firefighters who worked both short and long seasons (49 days and 98 days per year, respectively) were exposed to increased lifetime doses of PM4 across all career durations (5-25 years).
  • Wildland firefighters were estimated to be at increased risk of lung cancer (8 to 43 percent) and cardiovascular disease (16 to 30 percent) mortality across all season lengths and career durations.
  • These findings suggest that wildland firefighters should reduce exposure to smoke in any way possible.

[pdf-embedder url=”” title=”wildland Firefighter Smoke Exposure Health Risk2020″]


For more information: Smoke — and the health of firefighters

Let’s be careful out there.

Mass Bird Die-Off Linked to Wildfires and Toxic Gases

Using observations from crowdsourced science and weather location data, researchers concluded that wildfires caused a mass die-off of birds in the western and central United States in 2020.

By Joshua Rapp Learn

After an abnormally large number of migratory birds turned up dead in people’s backyards in Colorado and other parts of western and central U.S. states, locals began to document their observations on a crowdsourced science platform called iNaturalist. Within the app, a special project was set up specifically for this die-off, which occurred in August and September 2020, so that records of the dead birds could be compiled together.

Around the same period as the birds’ deaths, more than 3 million hectares (7.8 million acres) of land burned, which resulted in habitat loss and the emission of toxic compounds that threaten the health of both avian species and humans. In addition, snowstorms struck parts of the Northwest in early September while these birds were in the midst of their annual migration. Some areas experienced temperature drops of as much as 40°C (72°F) in just a few hours.

Mountain Bluebird, male
Mountain Bluebird, male. Photo by Bill Gabbert.

Researchers heard of this die-off event and wanted to see whether there was a link between the birds’ deaths and the other major events (wildfires and snowstorms) occurring in the United States at the time. In a new study published in GeoHealth, Yang et al. used the iNaturalist data, which included recordings of a number of migratory species such as warblers, geese, hummingbirds, swallows, flycatchers, and sparrows. The scientists also studied map readings that showed where observations were taken on iNaturalist to compare the locations of the birds’ deaths with the locations of the wildfires and storms.

Their findings were starkly clear. “The wildfire and also the toxic air were the two factors that influenced the birds’ mortality,” said Anni Yang, a postdoctoral fellow in spatial ecology at Colorado State University and one of the study’s authors. There was a strong correlation between the observations of dead birds and wildfires and the toxic gases they produced, but not with the early winter storms.

“The birds are sensitive to the environment,” Yang said. The respiratory system of avian species in particular easily can be damaged by air pollution. Although wildfires have always occurred and birds have evolved to cope with them in some measure, the combination of climate change and decades of fire suppression in parts of the United States has led to fires that burn far hotter and larger than fires that burned in centuries past. The larger fires could cause problems that birds nowadays aren’t capable of dealing with.The researchers also discovered that there were some differences in local areas. In parts of California, for example, more bird deaths occurred farther from the wildfires. The reason could be secondary impacts of the fires affecting humidity levels, which could lead to the deaths of birds in hot, humid air over the ocean.The researchers also noticed other trends. Land cover had an impact on bird deaths; the data showed that more birds died in urban areas. According to the authors, the reason could be known issues that affect birds, such as building strikes. But Yang noted that this correlation may be slightly biased because of quarantining due to the pandemic. In other words, people were spending more time in urban areas and perhaps paying more attention to dead birds around their homes, which inadvertently may have boosted the numbers in cities compared with rural areas.Yang also suggested that the lack of correlation between bird deaths and the snowstorms could be explained by shortcomings in the crowdsourced science application. In that case, fewer people may have been going outside during the bad weather, which could translate to fewer observations of dead birds.

Yang said other local factors might have played roles in the deaths of some species. The researchers looked at all bird deaths equally, but different species could be affected in different ways by climate events like wildfire smoke or a snowstorm.

Rongting Xu, an ecosystem modeler at Oregon State University and another of the paper’s authors, said that it would be great to run the same study over multiple years, comparing the summer of 2020 with previous summers, for example, to see whether wildfires or early snowstorms in other years caused similar die-offs. Such long-term examinations could also reveal whether factors like climate change are playing a role in bird deaths, she said. (GeoHealth, 2021)

—Joshua Rapp Learn (@JoshuaLearn1), Science Writer

This article first appeared at EOS, Science News by AGU.
Citation: Learn, J. R. (2021), Mass bird die-off linked to wildfires and toxic gases, Eos, 102, Published on 26 March 2021.


Study found hazardous air quality conditions at fire camps in Oregon and California

Smoke exposure levels at the Creek Fire ranged from hazardous to unhealthy for 30 days

(From Bill: Wildland firefighters and people who live in areas where long-term fires are common, such as Northern California and the Northwest, know that smoke can persist for days or weeks and can cause or aggravate respiratory and other medical issues. But knowing it exists and having peer reviewed quantifiable data proving it is hazardous to health, are two different things. Science like this could lead to changes that may benefit firefighters and the general public.)

In September and October the Centers for Disease Control and Prevention (CDC) deployed two staff members to serve as air resource advisors at wildfires in Oregon and California.

Air resource advisors were fully integrated into the wildfire incident management teams to provide insights into understanding and predicting smoke exposure levels. The individuals interacted with stakeholders, including air quality regulators, fire personnel, public health practitioners, and community residents. A primary aspect of this engagement was to forecast smoke levels for areas immediately affected by fires and generate a daily smoke outlook to keep stakeholders informed about prevailing smoke levels. 2020 is the first year during which the CDC worked with the Interagency Wildland Fire Air Quality Response Program and deployed staff members as air resource advisors for wildfire incidents.

From August 31 to September 14, 2020, one CDC staff member supported wildfires in central Oregon’s Cascade Range east of Sisters, which included the Beachie Creek, Holiday Farm, Lionshead, and Riverside fires. Strong east winds across the Cascade Mountains resulted in more than 560,000 acres of fire growth from September 7 through 10.

satellite photo fires smoke Washington, Oregon, and California
GOES-17 photo of smoke from wildfires in Washington, Oregon, and California at 5:56 p.m. PDT Sept. 8, 2020. The photo was taken during a very strong wind event.

Another CDC staff member was deployed to the Creek Fire from September 20 to October 5, 2020. This fire near North Fork, California started September 4 and grew to 193,000 acres during its first week; as of December 3, 2020, the fire had burned 379,895 acres.

Air quality study, fire camps, 2020
Abbreviation: PM2.5 = particles with aerodynamic diameters ≤2.5 μm.
       * Sensitive groups include persons aged ≤18 years; adults aged ≥65 years; pregnant women; persons with chronic health conditions such as heart or lung disease, including asthma and diabetes; outdoor workers; persons experiencing homelessness, and those with limited access to medical care. (
       † Fire camps typically offer logistical support to the wildfire suppression operation by providing firefighters and incident personnel sleeping locations (camping), morning and evening meals, workspaces, and administrative services.
       § The monitoring instrument in North Fork, California, recorded errors and did not report data during September 12–15, 2020.
       ¶ Start date of Creek Fire in California was September 4. Start dates of fires in Oregon were as follows. Lionshead was August 16; Beachie Creek was August 16; Holiday Farm was September 7; Riverside was September 8.

During these two deployments, several public health concerns came to light. Of note, although smoke from wildfires drifted long distances and affected downwind communities, the brunt of poor air quality was observed in communities adjacent to wildfire incidents. For example, communities near the fires in California and Oregon experienced high concentrations of PM2.5, as measured by air quality monitors, resulting in “Unhealthy” to “Hazardous” conditions, as defined by the U.S. Environmental Protection Agency Air Quality Index.

Fire personnel who camped and rested between work shifts at nearby fire camps (North Fork, California and Sisters, Oregon) were also exposed to poor air quality levels. These fire camp exposures contribute to higher overall cumulative smoke exposure and, along with other occupational risk factors such as fatigue and stress, could limit recovery that is much needed for fire personnel while away from the active fire perimeter. In addition, environmental hazards such as extreme heat and higher concentrations of ambient carbon monoxide were prevalent during days with heavy smoke and after extreme fire growth days. These hazards added a layer of complexity to fire response efforts and might have limited fire personnel recovery between work shifts.

From: Navarro K, Vaidyanathan A.  — Notes from the Field: Understanding Smoke Exposure in Communities and Fire Camps Affected by Wildfires— California and Oregon, 2020. MMWR Morb Mortal Wkly Rep 2020;69:1873–1875. DOI:

Thanks and a tip of the hat go out to Bob.

Smoke — and the health of firefighters

smoke pyrocumulus bushfires Australia
Photo of smoke from bushfires by Merrin Macleod on a flight from Canberra to Melbourne, Australia, posted January 4, 2020.

Originally published by the Centers for Disease Control and Prevention

While research has not yet been conducted on all the hazards and risks associated with the wildland firefighting job, the National Institute for Occupational Safety and Health (NIOSH) is asked numerous questions about the hazards of fighting wildland fires. This blog is designed to answer some of those questions.

What Is in Wildland Fire Smoke?

Wildland fire smoke is a mixture of gases and particles such as carbon monoxide (CO) and respirable particulate matter (PM) that may cause short- and long-term health effects. Wildland firefighters can be exposed to smoke at wildfires and “prescribed” fires (planned and intentionally ignited low-intensity fires). The contents of and exposure to wildfire smoke can vary greatly throughout the day depending on the vegetation type, fire behavior, and meteorological conditions. Research has shown that wildland firefighters have been exposed to gases and particles such as CO and PM above the occupational exposure limits during both wildland and prescribed fires. While burning vegetation is the primary exposure of concern for wildland and prescribed fires, when fires burn in the wildland urban interface (WUI, where wildland vegetation and urban areas meet) the smoke may contain compounds that are more similar to what structural firefighters encounter. Wildland firefighters will often suppress these fires and may be exposed to some of the hazardous compounds of WUI smoke such as volatile organic compounds (VOCs), flame retardants, and polycyclic aromatic hydrocarbons (PAHs). However, wildland firefighters do not have the benefit of wearing some of the personal protective equipment (PPE) typically used in a structural response (e.g., self-contained breathing apparatus [SCBA], turnout gear) that could provide protection from these compounds. Additionally, wildland firefighters may be exposed to smoke at firefighting base camps (incident command posts) where they eat and rest while off-duty.

What Do We Know About the Health of Wildland Firefighters?

Cardiovascular and Lung Health

In the past decade, several studies have linked exposure to wildfire smoke to short-term health effects, such as increases in inflammation and respiratory effects, for example, lung function decline.[i] However, these studies have only examined the health effects across a few shifts or a single fire season. It is not clear if these adverse health effects continue after fire season and whether they worsen after several seasons of fighting fires. Researchers suspect that exposure to particulate matter and other contaminants from wildfire smoke, heavy physical exertion, existing health and behavior risk factors, and cardiovascular strain could contribute to sudden cardiac events for wildland firefighters. Recent research indicated that wildland firefighters may be at an increased risk of mortality from cardiovascular disease and lung cancer than the general public from career exposure to wildfire smoke.[ii]


The strenuous work, long work shifts, close living and working conditions, limited access to hygiene supplies, and a workforce that responds to incidents all over the country on short notice to wildland fire incidents may be conducive for the transmission of infectious diseases, including SARS-CoV-2. Exposure to air pollutants in wildfire smoke can irritate the lungs, cause inflammation, alter immune function, and increase susceptibility to respiratory infections, possibly including COVID-19.[iii] In addition to potentially making firefighters more vulnerable to getting COVID-19, inflammation in the respiratory tract due to wildfire smoke might also increase the risk of developing more severe outcomes for those with COVID-19.[iv] Wildland firefighters should implement the recommendations described in the CDC’s FAQ for Wildland Firefighters to prevent infection and spread of COVID-19.

Heat-Related Illness and Rhabdomyolysis

Due to the nature of their work, firefighters are at risk of developing severe heat-related illness (such as heat stroke) and rhabdomyolysis (muscle breakdown).[v],[vi] Delays in diagnosis and initiating treatment of these illnesses increase the risk of permanent muscle damage. Since 2010, 62 cases of severe rhabdomyolysis among wildland firefighters have been reported to a passive surveillance system designed to capture fatalities and certain types of injuries and illnesses including rhabdomyolysis. The actual number of cases is likely higher due to underreporting and inconsistencies in reporting requirements and systems. Prior to 2010, no cases were reported.


Wildland firefighters work around power tools and heavy equipment that produce noise levels that are hazardous to hearing. In addition to hearing loss, noise exposure may also cause tinnitus (ringing/buzzing in ears), increased heart rate, fatigue, and interfere with verbal communication. Researchers from NIOSH and the United States Forest Service (USFS) evaluated personal noise measurements on 156 wildland firefighters conducting various training and fire suppression tasks, and reported that 85 of the 174 measurements were above the NIOSH maximum allowable daily dose[vii]. A follow-up study showed use of hearing protection was mixed; while almost all the wildland firefighters were aware of the noise in their environment and potential risk, very few were enrolled in hearing conservation programs.

What Are NIOSH Researchers Doing to Better Understand Exposures and Health Effects?

NIOSH is currently conducting research to understand the exposures and health effects of firefighters suppressing wildland and WUI fires. NIOSH researchers and collaborators at the US Forest Service and Department of the Interior have finished the second year of a multi-year study investigating exposures and health effects among six federal 20-person firefighting crews. The primary goal of this study is to measure exposures in the wildland fire environment and examine associations between those exposures and changes in lung, cardiac, kidney, and hearing function during each fire season and the off season over multiple fire seasons. This study has been paused in 2020 due to COVID-19 but is expected to resume.

To understand exposures and health effects faced by WUI firefighters, NIOSH is working with researchers from the University of Arizona and University of Miami to expand an existing collaborative research study (the Fire Fighter Cancer Cohort Study) to collect data regarding exposures from WUI fire incidents during the 2019 and 2020 fire seasons. Characterizing the types of chemicals, as well as the routes and levels of exposures, will help us understand health risks for wildland firefighters.

NIOSH is also in the process of developing a study assessing self-reported exposures to wildfire smoke and COVID-19 health outcomes among wildland firefighters. Additional information about this research will be available soon on the NIOSH Fighting Wildfires Page.


Authors of this article:

LCDR Corey Butler,MS REHS, is a Lieutenant Commander with the United States Public Health Service and an Occupational Safety and Health Specialist in the NIOSH Western States Division.

CAPT Christa Hale,DVM, MPH, DACVPM (Epi), is a Captain with the United States Public Health Service and Senior Epidemiologist and Veterinarian in the NIOSH Western States Division.

Kathleen Navarro, PhD, MPH is an Associate Service Fellow with the Division of Field Studies and Engineering.

Elizabeth Dalsey, M.A., is a Health Communication Specialist in the Western States Division.

CAPT Chucri (Chuck) A. Kardous, MS, PE, is a Captain with the United States Public Health Service and a research engineer with the NIOSH Division of Field Studies and Engineering.

Pamela S. Graydon, MS, COHC, is an Electronics Engineer working in hearing loss prevention in the NIOSH Division of Field Studies and Engineering. 

CAPT David C. Byrne, Ph.D., CCC-A, is a Captain with the United States Public Health Service and a research audiologist with the NIOSH Division of Field Studies and Engineering.


[i] Adetona O, Reinhard T, Domitrovich J, Boryles G, Adetona A, Kleinman M, Ottma R, Naher L [2016]. Review of the health effects of wildland fire smoke on wildland firefighters and the public. lnhal Toxicol 28(3): 95-139. Available from:

[ii] Navarro K, Kleinman M, Mackay C, Reinhardt T, Balmes J, Broyles G, Ottmar R, Naher L, Domitrovich J [2019]. Wildland firefighter smoke exposure and risk of lung cancer and cardiovascular disease mortality. Environ Res 173:462-468. Available from:

[iii] Reid CE, Maestas MM. Wildfire smoke exposure under climate change: impact on respiratory health of affected communities. Curr Opin Pulm Med 2019;25:179–187.

[iv] Moore JB, June CH. Cytokine release syndrome in severe COVID-19Science 2020;368:473.

[v] West MR, Costello S, Sol JA, Domitrovich JW [2020]. Risk for heat-related illness among wildland firefighters: job tasks and core body temperature change. Occup Environ Med77(7):433-438. Available from:

[vi] NIOSH [2012]. Report of a NIOSH health hazard evaluation, HHE 2011–0035. By Eisenberg J and McFadden J. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. Unpublished.

[vii] Broyles G, Butler C, Kardous C [2017]. Noise exposure among federal wildland fire fighters. J Acoust Soc Am 141(2) EL177. Available from:

Breathing smoke

October 4, 2020   |   6:09 a.m. PDT


Photographers at a wildland fire may be able to use and tolerate a mask that traps 95 percent of the 0.3 micron particulates in smoke, but the devices are not practical for firefighters. (see photo above)

In case you are wondering, masks and respirators are divided into rating classes: N is not oil resistant, R is oil resistant, and P is oil proof. The number, such as 95, refers to the percent of particles removed that are at least 0.3 microns in diameter.

Be careful out there.