Burn pits were large open-air waste disposal sites used by the U.S. military at bases across Iraq, Afghanistan, and other conflict zones, where everything from food scraps and human waste to plastics, electronics, rubber, munitions, and medical supplies was set on fire, often with jet fuel as an accelerant. The smoke they produced was a complex cocktail of toxic chemicals, and hundreds of thousands of service members lived and worked downwind of them for months or years at a time. Research into their health effects is still evolving, but the evidence now links burn pit exposure to a range of respiratory diseases, cardiovascular problems, neurological symptoms, and potentially cancer.
What Burn Pits Were and Why They Existed
At the height of U.S. operations in Iraq and Afghanistan, military bases generated enormous volumes of waste with no municipal infrastructure to handle it. The expedient solution was to dig a large trench, dump the waste in, douse it with fuel, and light it. Some of these pits operated around the clock for years. Joint Base Balad in Iraq, one of the largest U.S. installations in the country, ran a burn pit that at its peak consumed an estimated 200 tons of waste per day. Dozens of other bases used similar setups of varying scale.
The contents of these pits were staggeringly diverse. Materials included human and food waste, plastics, electronics, rubber, wood, fuels, metals, munitions, and industrial chemicals.1PubMed Central. Military burn pit exposure and airway disease: implications for our Veteran population Unlike a regulated incinerator, which burns waste at controlled temperatures with emission-scrubbing equipment, an open-air pit burns inefficiently and at variable temperatures. That incomplete combustion is precisely what makes the emissions so hazardous, because low-temperature burning of mixed materials generates a wider array of toxic byproducts than a hot, controlled flame would.
What Was in the Smoke
Laboratory simulations that burn mixtures of wood, rubber, plastic, and jet fuel to replicate burn pit conditions have confirmed that the resulting smoke is a complex stew of volatile organic chemicals, polycyclic aromatic hydrocarbons, and fine and ultrafine particles.2PubMed Central. Inhalation exposure to surrogate military burn pit emissions impairs systemic microvascular function: linking pulmonary insult and diverse peripheral responses A 2020 National Academy of Sciences report catalogued the specific hazards further, identifying various silicates and heavy metals, carbonaceous particulates, and additional volatile organic compounds.3PubMed Central. Quantitative lung particulate analysis links increased anthracotic pigment burden to burn pit exposure in post-9/11 veterans with distal lung disease Chemical speciation studies have also detected formaldehyde and acetaldehyde, both recognized as potential human carcinogens.4PubMed Central. Establishing a novel combustion generator system to simulate and study emissions from diverse applications
Air sampling at Joint Base Balad in 2007 added a real-world dimension to these lab findings. Burn pit emissions were the single most important source of dioxins and furans on base, accounting for about three-quarters of those compounds in the air, while vehicle engine exhaust was the primary driver of polycyclic aromatic hydrocarbons.1PubMed Central. Military burn pit exposure and airway disease: implications for our Veteran population Dioxins are particularly worrying because they are persistent, meaning they do not break down quickly in the body or the environment, and they are linked to cancer, immune dysfunction, and reproductive harm.
Fine particulate matter smaller than 2.5 micrometers is another major component of burn pit smoke. Particles that small can bypass the nose and upper airways entirely and lodge deep in the lungs, where they trigger inflammation. Animal studies have shown that particulate matter from simulated burn pit emissions significantly increases lung injury.1PubMed Central. Military burn pit exposure and airway disease: implications for our Veteran population That kind of deep-lung inflammation is the starting point for several of the diseases now being diagnosed in exposed veterans.
Constrictive Bronchiolitis and Other Lung Diseases
The respiratory condition most closely tied to burn pit exposure is constrictive bronchiolitis, a disease in which the tiny airways deep in the lungs become scarred and narrowed, permanently restricting airflow. It does not show up reliably on standard breathing tests or chest X-rays, which has made it easy to miss or misdiagnose as ordinary asthma. The landmark study that brought it to public attention examined 49 soldiers returning from Iraq and Afghanistan with unexplained breathing problems. Every one of their lung biopsies was abnormal, and 38 of the 49 had changes diagnostic of constrictive bronchiolitis.5PubMed Central. Constrictive bronchiolitis in soldiers returning from Iraq and Afghanistan
Subsequent case series have reinforced the pattern. Clinicians have documented multiple veterans, ranging in age from their mid-thirties to their sixties, who served in Iraq or Afghanistan and were exposed to burn pits, only to develop progressive shortness of breath, chronic cough, and exercise intolerance. Biopsies in these cases confirmed constrictive bronchiolitis, sometimes accompanied by other scarring patterns like chronic adhesive pleuritis.6American Journal of Respiratory and Critical Care Medicine. B30-11 Case Series of Constrictive Bronchiolitis in Veterans Deployed to Southwest Asia Imaging research is now trying to develop ways to detect deployment-related constrictive bronchiolitis using quantitative CT scans rather than invasive biopsies, comparing the lung scans of veterans with biopsy-proven disease against both symptomatic veterans and healthy civilians.7PubMed Central. Use of quantitative CT chest imaging to derive and assess a radiographic phenotype of deployment-related constrictive bronchiolitis
Constrictive bronchiolitis is not the only respiratory problem. Analysis of a large military cohort found that deployment to Iraq and Afghanistan significantly increased the risk of new-onset asthma, with up to 14 percent of deployed personnel developing it. Combat exposure independently raised that risk by roughly a quarter.1PubMed Central. Military burn pit exposure and airway disease: implications for our Veteran population
It Is Not Just the Lungs
Burn pit smoke does not stay confined to the respiratory tract. The upper airways take a hit too. A study comparing veterans deployed to bases with burn pits against those deployed without such exposure and those never deployed found that chronic rhinosinusitis with nasal polyps was about three times as common in the burn-pit-exposed group, affecting roughly 28 percent of them compared with under 9 percent in the other groups.8PubMed Central. Burn pit exposure is associated with increased sinonasal disease Chronic sinusitis may sound minor compared with a scarred lung, but it brings persistent congestion, facial pain, impaired smell, repeated infections, and often surgical intervention.
There is also emerging evidence that the fine and ultrafine particles in burn pit smoke cause systemic damage beyond the airways. Animal experiments using surrogate burn pit emissions have found that inhalation impairs microvascular function throughout the body, not just in the lungs.2PubMed Central. Inhalation exposure to surrogate military burn pit emissions impairs systemic microvascular function: linking pulmonary insult and diverse peripheral responses That finding matters because microvascular dysfunction is a precursor to cardiovascular disease, and the epidemiological data increasingly reflect a cardiovascular signal in exposed veterans.
Cardiovascular Effects and Hypertension
A large study published in JAMA Network Open found that the duration of deployment to bases with open burn pits was associated with higher rates of hypertension. Veterans in the highest exposure group had about a 10 percent increased odds of hypertension compared with those without burn pit exposure, and the risk climbed in a dose-response pattern: the longer you were there, the higher the risk. There was also an elevated risk of ischemic stroke, though the data on stroke were less precise. Other cardiovascular outcomes like coronary artery disease did not show a clear link.9PubMed Central. Deployment to Military Bases With Open Burn Pits and Respiratory and Cardiovascular Disease
A follow-up analysis added an important nuance: the type of waste being burned mattered. Deployment to bases that burned unsegregated waste, meaning everything went into the pit together, was associated with elevated risks of both hypertension and asthma. But deployment to bases that segregated their waste or used incinerators instead of open pits was not. For those with the longest exposure to unsegregated burning (more than 240 days), the risk of hypertension was about 16 percent higher than for those never stationed at such bases.10PubMed Central. The impact of burn pit waste segregation practices on respiratory and cardiovascular health risks among US military veterans deployed to Iraq and Afghanistan This finding reinforces the idea that the chemical complexity of the smoke, driven by the variety of materials burned, is central to the health risk. Burning just wood or food waste in the open is bad, but it is nowhere near as hazardous as burning an unsorted mix of plastics, electronics, chemicals, and medical waste.
Neurological Symptoms and Pain
Veterans exposed to burn pits report neurological symptoms at notably higher rates than unexposed veterans. A study of veterans using non-VA private healthcare found that burn-pit-exposed individuals had significantly higher odds of numbness in the arms and legs, aching limb pain, and burning limb pain. The odds of burning pain in particular were more than three times higher in the exposed group.11PubMed Central. Prevalence of Burn Pit Associated Symptoms Among US Veterans Who Utilize Non-VA Private Healthcare A broader review of the literature likewise found that reported symptoms range from respiratory problems to neurological deficits, though treatment pathways have been limited partly because VA medical facilities historically required proof that a condition was service-connected before offering certain benefits.12Frontiers in Environmental Health. Burn pit exposure in military personnel and the potential resulting lung and neurological pathologies
The mechanism behind neurological damage from burn pit smoke is not fully understood, but it is biologically plausible. Several of the compounds in burn pit emissions, including heavy metals and certain volatile organic chemicals, are known neurotoxins. Ultrafine particles can also cross from the lungs into the bloodstream and, in some cases, cross the blood-brain barrier. Research on civilian air pollution has established similar pathways between fine particulate exposure and neurological harm, and the concentration of toxins in burn pit smoke far exceeds typical urban air pollution levels.
Cancer Concerns
Cancer is the health outcome that generates the most anxiety among exposed veterans, and the one where the evidence remains most incomplete. The mix of carcinogens in burn pit smoke, including dioxins, polycyclic aromatic hydrocarbons, formaldehyde, and heavy metals, makes a cancer link theoretically plausible. But cancer takes years or decades to develop, and the deployed population is still relatively young, so the epidemiological picture is unfinished.
One of the few long-term follow-ups to look at cancer focused on Gulf War veterans potentially exposed to hazardous demolitions at Khamisiyah, Iraq. Over a 21-year period, those with two or more days of estimated exposure had a risk of brain cancer death that was about 72 percent higher than unexposed veterans. However, the finding was not statistically significant, meaning it could have been due to chance, and the exposure was not specifically to burn pits but to a demolition site where nerve agent byproducts may have been released.13PubMed Central. Trends in brain cancer mortality among U.S. Gulf War veterans: 21 year follow-up The PACT Act of 2022, discussed below, effectively resolved the policy question by presuming that certain cancers are connected to burn pit exposure for benefits purposes, even while the epidemiological studies continue to accumulate data.
Mental Health and Injury-Related Mortality
Burn pit exposure does not exist in isolation. The veterans who breathed the smoke were also in combat zones, experiencing trauma, sleep deprivation, and physical strain. Untangling which health effects come from the smoke and which from the broader deployment environment is one of the central challenges researchers face. A recent study found that cumulative deployment duration to bases with open burn pits was associated with increased risk of post-traumatic stress disorder, intracranial injuries, and unintentional injury-related mortality.14PubMed. Deployment to Military Bases With Open Burn Pits and Mental Health Conditions and Injury Mortality Among US Veterans Whether the burn pit exposure itself contributes to these outcomes through neurological pathways, or whether it is acting as a proxy for intensity and duration of combat deployment, remains an open question. The practical result for veterans is the same either way: longer time at these bases correlates with worse outcomes across both physical and mental health domains.
Sleep problems also appear to be pervasive. Data from the VA’s Airborne Hazards and Open Burn Pit Registry show that symptoms associated with sleep apnea are reported by over half of registrants, and insomnia symptoms by about 80 percent. Yet formal medical diagnoses lag far behind: only about 32 percent had a sleep apnea diagnosis in their medical records, and fewer than 18 percent had an insomnia diagnosis. The mismatch suggests that many veterans with significant sleep disturbances are not being identified or treated through the formal healthcare system.15PubMed Central. Concordance Between Self-Report and Electronic Medical Record Diagnoses of Insomnia and Sleep Apnea: Lessons From the Airborne Hazards and Open Burn Pit Registry
What the Evidence Does Not Show
Not every health concern investigated has panned out. A prospective study of chronic multisymptom illness, a broad category covering fatigue, pain, and cognitive difficulties, found no elevated risk among service members deployed to three bases with documented burn pits compared with other deployed personnel, after adjusting for confounding factors.16PubMed. Prospective assessment of chronic multisymptom illness reporting possibly associated with open-air burn pit smoke exposure in Iraq This does not mean that exposed veterans feel fine. It means that when researchers used the broad umbrella of multisymptom illness as the outcome measure and tried to isolate burn pit smoke from the many other stressors of deployment, the signal disappeared. The more specific outcomes, like constrictive bronchiolitis or hypertension, show clearer associations than the catch-all categories.
Similarly, an investigation into whether burn pit or airborne hazard exposure worsened long COVID outcomes found no increased risk. Among a sample of over 200 veterans in the burn pit registry who developed COVID-19, neither burn pit exposure nor broader airborne hazard exposure increased the odds of post-acute sequelae of SARS-CoV-2.17PubMed Central. Prevalence and risk factors of post-acute sequelae of SARS-CoV-2 (PASC) among veterans in the airborne hazards and open burn pit registry: a prospective, observational, nested study And sarcoidosis, a granulomatous lung disease that some advocates suspected might be linked to burn pit smoke, turned out to be an uncommon diagnosis among registry participants. The only deployment-related exposure marginally associated with sarcoidosis was convoy activity, not burn pit proximity.18PubMed Central. Factors associated with a diagnosis of sarcoidosis among US veterans of Iraq and Afghanistan
These null findings are actually useful. They help sharpen the picture of what burn pit smoke does and does not do, which in turn helps clinicians focus screening and treatment resources on the conditions where the evidence is strongest.
The PACT Act and What Changed for Veterans
For years, veterans who believed their illnesses were caused by burn pit exposure faced an uphill battle getting the VA to acknowledge the connection. The burden of proof fell on the individual veteran to demonstrate that a specific condition was service-connected, which was nearly impossible for diseases with long latency periods and complex causation. The Sergeant First Class Heath Robinson Honoring Our Promise to Address Comprehensive Toxics (PACT) Act, signed into law in August 2022, fundamentally changed the landscape. It expanded VA healthcare eligibility for veterans exposed to burn pits and other toxic substances, created a presumption of service connection for over 20 conditions including several cancers and respiratory illnesses, and extended the window for veterans to enroll in VA healthcare after leaving the military.
The law also mandated the continuation and expansion of the Airborne Hazards and Open Burn Pit Registry, a voluntary database that veterans can join to document their exposures and health concerns. The registry has become a crucial research tool, providing the data that many of the studies cited throughout this article draw upon. It also functions as a screening mechanism: veterans who enroll are invited to a clinical evaluation, which sometimes catches conditions that would otherwise go undiagnosed.
Emerging Research Frontiers
One of the more intriguing recent findings involves the lung microbiome. Animal experiments exposing subjects to burn pit emissions found that the inhalation produced distinct and significant changes in the microbial populations living in the lungs, creating a kind of microbial signature specific to burn pit smoke exposure.19PubMed Central. In vivo lung microbiome alterations from burn pit emissions and/or sand inhalation exposures This is early-stage research, but if the findings translate to humans, lung microbiome analysis could eventually serve as a biomarker to confirm burn pit exposure in veterans whose deployment records are incomplete or whose exposure was never formally documented.
Lung tissue studies are also advancing. Quantitative analysis of lung biopsy samples from post-9/11 veterans with distal lung disease has found increased anthracotic pigment, the dark particulate deposit that accumulates in lung tissue from inhaled combustion products. Veterans with documented burn pit exposure showed a higher burden of this pigment than would be expected for their age and smoking history, providing a physical trace of the exposure embedded in the tissue itself.3PubMed Central. Quantitative lung particulate analysis links increased anthracotic pigment burden to burn pit exposure in post-9/11 veterans with distal lung disease Taken together, these lines of investigation are slowly building the kind of objective, biological evidence that both clinicians and disability evaluators need to move beyond reliance on self-reported exposure histories alone.