Wildfire smoke alters immune cells, promoting inflammation

Smoke Beaver Fire
Smoke at the Beaver Fire in Northern California, August 12, 2014. Photo by Bill Gabbert.

Immune cells that normally protect against inflammation and infections can be altered by wildfire smoke to promote inflammation. A long list of diseases are associated with  inflammation. Studies have shown that healthy individuals and those with pre-existing conditions are affected by the very small PM2.5 particles produced by wildfire smoke.

forecast 4 a.m. PDT October 26 fire wildfire smoke
Forecast for the distribution of smoke at 4 a.m. PDT October 26, 2019 in the San Francisco area and south as far as Santa Maria.

Below are excerpts from an article written by Tori Rodriguez first published in Pulmonology Advisor. It covers the effects of smoke on humans and suggests what could be done to mitigate the potential damage. One idea is for fire and local officials when considering evacuation guidelines to plan for not only the dangers of flames, but also the effects of smoke.

[With wildfires increasing] and the health issues that result, there is a real and growing need for clinicians to educate at-risk patients, according to Jennifer Stowell, PhD, a postdoctoral researcher in the department of environmental health at the Boston University School of Public Health and co-author of a recent study on the health effects of wildfires.2 “For clinicians, education of patients is paramount, especially for those with already compromised health,” said Dr Stowell.

Healthy individuals may also experience health consequences from wildfires, according to Angela Haczku, MD, PhD, professor of medicine at the University of California, Davis, School of Medicine and director of the UC Davis Lung Center. “During the 2020 California wildfire season, my team conducted a study on healthy individuals and found alarmingly increased numbers of abnormal, activated immune cells in the peripheral blood.3 These cells are normally responsible for protecting against inflammation and infections, but when altered by inhalation of wildfire smoke, they become the ones promoting inflammation,” she explained.

Research exposes burning issues

The vast majority of recent US wildfires have been concentrated in western states, including Washington (218 fires), California (153 fires), Montana (141 fires), and Utah (130 fires).Estimates show that more than 70,000 wildfires have burned an average of 7 million acres in the US annually since the year 2000.4

In addition to this geographic damage, a sizeable body of research has detailed the negative human health effects resulting from exposure to wildfire smoke:

  • In a study published in June 2022, Heaney et al found that “smoke event” days —  those with the highest amounts of particulate matter 2.5 (PM2.5) from wildfires — were linked to increases in unscheduled hospital visits in California for all respiratory diseases (3.3%; 95% CI, 0.4%-6.3%) as well as asthma specifically (10.3%; 95% CI, 2.3%-19.0%), with the largest effect observed among children ages 0 to 5 years with asthma.2

Stratified analyses demonstrated increased visits for all cardiovascular diseases, ischemic heart disease, and heart failure among non‐Hispanic White patients and individuals older than 65 years. The findings further suggested that the interaction between wildfire PM2.5 concentrations and high temperatures may further increase the need for hospital visits among patients with cardiovascular disease.

  • A 2022 scoping review found evidence of increased population-level mortality, respiratory morbidity, and rates of various types of cancer in association with exposure to PM2.5 and chemicals from wildfire smoke.5
  • Findings from a 2021 study indicate that particulate matter from wildfire smoke has a greater effect on respiratory health than particulate matter from other sources of emission, based on a comparison of the increase in respiratory hospitalizations associated with increases in wildfire-specific PM2.5 (increase in hospitalizations ranging from 1.3% to 10%) and non-wildfire PM2.5 (increase in hospitalizations from 0.67% to 1.3%) in Southern California.6
  • Research published in 2021 showed that a 10 µg/m3 increase in wildfire PM2.5 was correlated with increased hospitalizations for all respiratory diseases, asthma, chronic obstructive pulmonary disease (COPD), and ischemic heart disease in Colorado. Wildfire PM2.5 was also associated with an increase in deaths due to asthma and myocardial infarction.7
  • Other results reported in 2021 linked wildfire PM.2.5 exposure in Alaska to elevated odds of asthma-related emergency department (ED) visits among various population, with odds ratios ranging from 1.10 (95% CI, 1.05-1.15) to 1.16 (95% CI, 1.09-1.23).8
  • A 2018 study analyzed data pertaining to 21,353 inpatient hospitalizations, 25,922 ED presentations, and 297,698 outpatient visits during periods of heightened smoke exposure from the 2007 San Diego wildfires. The results demonstrated a 34% increase in ED visits for respiratory diagnoses and a 112% increase in ED visits for asthma. Even greater increases in ED visits were observed among children aged 0 to 4 years with respiratory diagnoses  (73% increase) and in children aged 0 to 1 year with asthma (243% increase).9
  • Studies have also demonstrated increases in ED visits and hospitalization rates for asthma and other respiratory diseases in relation to wildfire PM2.5 in states such as Oregon and Nevada.10,11
  • Additionally, findings from multiple studies point to a potential connection between wildfire smoke exposure and higher rates of COVID-19 infection and associated mortality. In 1 study, researchers found that COVID-19 cases and related deaths increased by 56.9% and 148.2%, respectively, after the onset of the California wildfires that began in September 2020 compared with the period of time from the onset of the pandemic to just before the wildfires began.12
  • Results of another recent study suggest that “wildfire smoke inhalation sequesters activated, pro-inflammatory [natural killer] cells to the affected tissue compartments and may interfere with [COVID-19] vaccine effectiveness,” according to the authors.13

We interviewed Drs Stowell and Haczku to find out more about what clinicians need to know about the health effects of wildfires. Notably, Dr Haczku recently chaired the 2022 third annual NorCal Symposium on Climate, Health, and Equity.

“The size of the particulate matter is important….Particles larger than 10 micrometers in diameter are deposited in the nose, mouth, and upper airways, while PM2.5 is sucked directly down to the alveoli…causing disruption and inflammation.”
Dr Angela Haczku, Director of the University of California Davis Lung Center and chair of the 2022 NorCal Symposium on Climate, Health, and Equity.

What is known about the health effects of exposure to wildfire smoke?

Dr Stowell: Several studies have investigated the health effects of wildfire smoke and have linked smoke exposure to respiratory disease, cardiovascular disease, and birth outcomes such as preterm birth and low birth weight.14 Several gaps remain, including a better understanding of indoor air quality during wildfire events, the risk to outdoor workers, pregnancy complications, and mental health.

Dr Haczku: Wildfire smoke contains particulate matter of varying sizes, usually classified into PM10 and PM2.5 and ozone (O3) and nitrogen-containing toxic gases. All of these are combined with volatile organic chemicals that fuel the flames, the quality and quantity of which depend on whether what is burning comes from wild land, urban areas, or combined areas.

The size of the particulate matter is important because it determines where in the respiratory tract it will end. Particles larger than 10 micrometers in diameter (PM10) are deposited in the nose, mouth, and upper airways, while PM2.5 is sucked directly down to the alveoli, the tiny sacs responsible for our breathing, causing disruption and inflammation.

These particles are also carriers of inflammatory, allergenic, infectious, and toxic molecules causing both acute and chronic illnesses.

The most affected and best-studied organs susceptible to wildfire smoke are the respiratory tract and the cardiovascular system. Most ED visits are related to exacerbations of asthma and COPD and heart conditions such as coronary disease. Respiratory and cardiovascular mortality and hospitalization rates are well-known to be increased during wildfires. Affected adults and children also often suffer from anxiety and other mental health conditions. These conditions and the long-term health effects of wildfires are less studied and poorly understood.

What are the implications of these effects for health care systems?

Dr Stowell: Increasing wildfire activity due to climate change will continue to exacerbate these issues. Wildfire smoke exposure used to be thought of as an issue for the western US. However, as seen in the past several years, smoke from large fires and complex fires can reach across the continental US, exposing many individuals to harmful pollutants. Even with this wider spread of smoke, exposure will continue to have the greatest effect on the health of communities close in proximity to the fires, where smoke density is the heaviest.

Often the communities most affected are rural and face distance barriers to accessing proper health care. Thus, the health care systems in these already underserved areas could face capacity and response issues as wildfire smoke exposure continues to increase in western US states.

Dr Haczku: The effect of wildfire smoke on respiratory, cardiovascular, mental, and general health could be alleviated through specific interventions. As such, wildfire-related disasters provide health care systems with an opportunity to take a proactive role. Health care professionals should strategically and intentionally prepare for wildfire smoke events. Educational material should be prepared using professional society-approved guidelines and toolkits. These also need to be translated into the languages of and distributed to patients and potentially affected communities as well as the general public.

Having an efficient local system in place for timely warnings to reduce time spent outdoors during wildfire smoke events is crucial. Preventive measures in schools and indoor public places such as improved air filtration systems should be installed.

What are recommendations or considerations for clinicians to keep in mind when caring for patients in areas most affected by wildfires?

Dr Stowell: Education of patients is paramount. Some other steps could include considering temporary staff increases during wildfire seasons, ensuring the clinic staff are well-educated regarding wildfire smoke safety measures, and partnering with communities to provide clean air options for their patients.

Dr Haczku: In addition to intensive management of risk factors and chronic diseases, I believe implementing preventive measures are the most important. For example, professionals need to make sure that timely public warnings of smoke events are in place. Clinicians and health care workers should have a database that can be used to identify and reach out to vulnerable populations including pregnant women, children, the elderly, and farm and construction workers. Education of these communities and individuals can prevent emergency situations. Susceptible patients suffering from chronic illnesses and workers who cannot avoid outdoor activities may require help with fitting personal respirators and devices and specific consultation by health care workers.

What broader measures are needed to buffer the effects of wildfire smoke exposure and protect vulnerable populations, such as those with respiratory and cardiovascular diseases?

Dr Stowell: Much more needs to be done to plan for these large fire events. This planning includes focusing efforts in the areas most often affected by smoke through increasing health care system capacity, forming mobile health response teams, proper community education, better guidelines for evacuation (as most evacuations are intended to avoid the flames and not the smoke). Another need is access to clean air options, such as providing clean air centers and affordable access to air purification technology, including air conditioning and HEPA filtration.

Dr Haczku: As a health care educator, administrator, and climate change researcher, I see an urgent unmet need for the education of health care professionals about the effects of wildfires and, more generally, of climate change on human health. Vulnerable subjects, especially patients suffering from chronic health conditions, should be identified and educated. Improving advocacy toolkits and updating evidence-based professional guidelines for disease management and preventive interventions to reduce risk and protect health is imperative.

Research efforts to study and better understand wildfire smoke-induced pathologies as well as research to investigate the effectiveness of novel interventions should be better supported.


  1. Fire, Weather, and Avalanche Center. Current wildfires burning in the U.S. Accessed September 11, 2022.
  2. Heaney A, Stowell JD, Liu JC, Basu R, Marlier M, Kinney P. Impacts of fine particulate matter from wildfire smoke on respiratory and cardiovascular health in CaliforniaGeohealth. 2022;6(6):e2021GH000578. doi:10.1029/2021GH000578
  3. Teuber M, Flayer C, Linderholm A, et al. Wildfire smoke exposure activates circulating innate immune cellsJ Allergy Clin Immunol. 2021;147(2);Suppl_AB237. doi:10.1016/j.jaci.2020.12.012
  4. Congressional Research Service. Wildfire Statistics. Updated September 2, 2022. Accessed September 30, 2022.
  5. Grant E, Runkle JD. Long-term health effects of wildfire exposure: A scoping reviewJ Climate Change Health. 2022;6:100110. doi:10.1016/j.joclim.2021.100110.
  6. Aguilera R, Corringham T, Gershunov A, Benmarhnia T. Wildfire smoke impacts respiratory health more than fine particles from other sources: observational evidence from Southern California. Nat Commun. 2021;12(1):1493. doi:10.1038/s41467-021-21708-0
  7. Magzamen S, Gan RW, Liu J, et al. Differential cardiopulmonary health impacts of local and long-range transport of wildfire smokeGeohealth. 2021;5(3):e2020GH000330. doi:10.1029/2020GH000330
  8. Hahn MB, Kuiper G, O’Dell K, Fischer EV, Magzamen S. Wildfire smoke is associated with an increased risk of cardiorespiratory emergency department visits in AlaskaGeohealth. 2021;5(5):e2020GH000349. doi:10.1029/2020GH000349
  9. Hutchinson JA, Vargo J, Milet M, et al. The San Diego 2007 wildfires and Medi-Cal emergency department presentations, inpatient hospitalizations, and outpatient visits: An observational study of smoke exposure periods and a bidirectional case-crossover analysis. PLoS Med. 2018;15(7):e1002601. doi:10.1371/journal.pmed.1002601
  10. Gan RW, Liu J, Ford B, et al. The association between wildfire smoke exposure and asthma-specific medical care utilization in Oregon during the 2013 wildfire seasonJ Expo Sci Environ Epidemiol. 2020;30(4):618-628. doi:10.1038/s41370-020-0210-x
  11. Kiser D, Metcalf WJ, Elhanan G, et al. Particulate matter and emergency visits for asthma: a time-series study of their association in the presence and absence of wildfire smoke in Reno, Nevada, 2013-2018. Environ Health. 2020;19(1):92. doi:10.1186/s12940-020-00646-2
  12. Meo SA, Abukhalaf AA, Alomar AA, Alessa OM, Sami W, Klonoff DC. Effect of environmental pollutants PM-2.5, carbon monoxide, and ozone on the incidence and mortality of SARS-COV-2 infection in ten wildfire affected counties in CaliforniaSci Total Environ. 2021;757:143948. doi:10.1016/j.scitotenv.2020.143948
  13. Sanghar GK, Ravindran R, Teuber MJ, et al. Phenotypic evaluation of natural killer (NK) cells in response to BNT162b2 mRNA Covid-19 vaccine during wildfire smoke exposure. Presented at: the American Thoracic Society (ATS) 2022 International Conference; May 13-18, 2022; San Francisco, CA. Abstract A5407. doi:10.1164/ajrccm-conference.2022.205.1_MeetingAbstracts.A5047
  14. Evans J, Bansal A, Schoenaker DAJM, Cherbuin N, Peek MJ, Davis DL. Birth outcomes, health, and health care needs of childbearing women following wildfire disasters: An integrative, state-of-the-science reviewEnviron Health Perspect. 2022;130(8):86001. doi:10.1289/EHP10544

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Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire.

21 thoughts on “Wildfire smoke alters immune cells, promoting inflammation”

  1. Finally information about the dangers of forest fire smoke is being disseminated. I contend that forest fire smoke is dangerous whatever type of forest fire it is coming from. “Prescribed”forest fire is just as dangerous as “wildfire”smoke. Prescribed forest fires extend the exposure time to smoke to almost 10 months. This has to stop.
    The “burning and clearing of forests needs to be reined in.

  2. Yep, I’m done. I will not lift a finger to help in any way with Rx. Nope. In fact, today, I asked (strongly) for my supervisor to completely remove RXB2 from my IQCS.
    Not getting cancer from a PLANNED event so some dildo fuels program manager can get a gold star and a cash award. Eff that!

  3. After seeing this.. F*ck this is running through my head. The supplement and all the good that may come doesn’t seem to justify it all. Summers gone, relationships tainted, and not much to show for it. I’d rather go out having a heart attack rowing my drifter, vs some messed up cancer I got as a participation trophy working for beans and rice.

    1. Amen Jon,
      if I can talk even one more person out of this fu—– job I will.
      I’ve seen my best bro almost die right in front of me to have another kill himself (suicide) the following winter. I have pleated with people to give this all up. You will be more of a human than you ever were once you leave- you will once again start to have emotions, perhaps feelings and you may even smile. This suck it up culture is never able to change. If you think about it wildland firefighters are treated no better than hard time prisoners (nothing against prisoners whatsoever). A guard or squad leader barking orders at you for 16-hour days 2-weeks straight with little to no breaks, sack lunches of crap, and mre’s (military rations) for days. Wait in line to poop in a porta potty that someone just missed and hit the rim. Seems like Groundhog Day the movie, over and over again but it’s not funny at all.
      Stand in line for chow at 0530 and get back around 2200 waiting in line for some summer camp kid to serve you and he doesn’t know anything about nutrition or being a chef. The work is almost as arduous as a chain gang building railroad line nonstop for years. Except the railroad is still standing or operating and those folks didn’t die from CANCER right after it was complete.

  4. Can someone tell me ONE positive part of being a Wildland Firefighter? or should we say 0462 Forestry Technicians. I can’t think of one positive aspect of this position anymore. It sucks to be a wildland firefighter.
    I am tired of the Rederick about my co-workers getting put in jail for doing his job, because of anti-government freaks. No thanks, I am done losing friends to this stupid job. I am tired of missing all my family gatherings year after year. I am tired of missing weddings and reunion’s because I am more worried about making money than being happy or having a support system. I’m just tired of living off catered food or military rations, which is worse than prison food, oh wait the prisoners make food for the firefighters in Nevada. I am exhausted from putting in miles upon miles of non-sense fire lines in the woods that will eventually get burned over anyway. When the ashes settle after 20 more years, what part of your health, or your friends, family will remain?? Please ask yourself that question.

  5. From a fire mgt career starting in 1960 with a 3-year break to serve in VN, I now am without a bladder/prostate from cancer. Back in the day, it was 21 day assignments, with Rx fire during the off-season. And upon returning from the ’88 fires in Yellowstone, suffered a heart attack. There’s a message in all that somewhere.

    So, was the culprit agent possibly orange? Or as mentioned the fine particulates in smoke? I can’t answer that, but I do support a lot more research, especially on firefighters.

    And kudos to Bill for putting some light on this important subject.

    1. I know of one guy who died of brain cancer and another fighting lymphoma, another has breast cancer-all career wildland firefighters. I guess I’m just playing the waiting game…

  6. Hmm, USDA and DOI only need look at wartime “airborne hazards and burn pit exposure” studies from the VA. Thankfully, after years of fighting for it, there is now legislation favoring compensation for those military veterans and workers who have suffered the consequences of having to breathe that toxic air while performing their duties. The similarities to the wildfire realm are uncanny. Yep, no doubt that there’s a lot more toxic substances in the smoke from wartime burn pits but the science on how the smoke particles trigger disease from increased inflammation is the same.

  7. I always charge H pay on Rx fires and my supervisor approves it. I approve it for my folks too. We’ve been doing it for years and it’s the right thing to do. We also ALWAYS file a CA-1 after burning to document smoke inhalation.

  8. Why don’t we require even basic respiratory PPE? We should outfit all firefighters with simple 60$ sundstrom OV/HC/P99 half masks that would help people breathe and maybe reduce some other health risks. We already have to wear hard hats, nomex, gloves, eye pro, ear pro, special boots. But no PPE for breathing in heavy smoke. Pretty wild. Even with one study after another saying, gee, wildfire smoke is really bad for you, and will take years off your life, as if that is even a question! Just order some masks!

    I already bought mine because I want to live as long as possible after I retire.

  9. I was diagnosed 17 years into my career with the FS. They believe it has a causal relationship well enough to approve FECA bulletin 22-07. I just can’t understand why we do not get h pay for prescribed fire. The physical danger may not be the same but the effects on health are probably worse.

    1. You can get HP for prescribed fire under certain circumstances. Just read the parent text in the CFR and USC and have a sympathetic boss.

    2. Michelle, I believe that is the DOL saying your cancer is related to your work. Good for them.

      The USFS/DOI are burying their heads in the sand, and killing their employees, because if they acknowledged a negative health impact they would have to mitigate the risk to their employees. It’s tough for the office goers in DC or at the regional offices that make these decisions when it really doesn’t impact them anymore. It also shows the kinds of people we promote, who seemingly don’t care about the people they used to be.

      1. Ben, according to the bulletin Non-Hodgkins Lymphoma is on the known cancers to be caused in this line of work. However, my case has yet to be approved. I am on my 3rd attempt.

        I am furious to know that all these studies exist out there that show how toxic our job is to human health and that in my 20-year career I’ve never been educated about the dangers of it. Why isn’t caution, may cause cancer on our RAWS?

        It’s mind baffling.

  10. The USFS/DOI do not acknowledge that smoke has any negative health impacts. I was told they don’t believe the studies done by Kat Navarro have enough participants to make any conclusions.

    There may be some studies occuring now that would allow the USFS/DOI to make a determination, but that is probably 5 years away.

    1. Chances are the USFS and DOI apparatchiks who fail to acknowledge the negative health impacts of wildfire smoke work out of air-conditioned offices in Washington D.C. They should have spent the last five summers in California breathing brown air and then they might possibly have a clue.

      You don’t have to be a fire fighter to be affected by the Forest Service’s pathetic enviro-driven policies to know that breathing this crap for at least two weeks every year isn’t good for a human being’s respiratory system. At one point this year the AQI number in my area was over 600 for several days because of smoke from the Mosquito Fire. Too bad I couldn’t have piped some of it to Forest Service headquarters in D.C. so they could get a taste of it.

      The USFS’ idiocy never ceases to amaze.

        1. How about ‘active forest management’, including (GASP!) thinning, biomass removal (chipping) and prescribed burns?
          Enviro-driven policies have been proven to be complete and utter failures that have resulted in millions of acres burned in catastrophic wildfires in the West. Many scientists have begun to realize this and are beginning to point this out. Some of those studies have been mentioned on this very website.

          By the way, how many critters do you suppose have been burned out of their habitat due to enviro-driven policies on those millions of acres burned?

          Not so fun fact- two thirds of the Mendocino National Forest have burned in the last 5 years, thanks to enviro-driven policies.


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