Wildfire smoke pouring in from Canada has recently interrupted daily life in the Midwest, the Northeast, and Mid-Atlantic regions. As climate change intensifies, wildfires are projected to become an ever-bigger problem, resulting in dangers to lung and cardiovascular health, increased mortality and morbidity, and mental health issues.

The effect of wildfire smoke on the lungs is of particular concern. Wildfire smoke is both dangerous and insidious to patients with pre-existing pulmonary conditions.

Toxicity Explained

Wildfire is an admixture consisting of carbon monoxide, fine particulate matter, nitrogen dioxide, sulfur dioxide, and volatile organic compounds. It can travel thousands of miles from the fire zone, as demonstrated most recently.1

Continue Reading

Fine particulate matter refers to particles with an aerodynamic diameter at least 2.5 μm (PM2.5). These small particles play a chief role in the negative health impact of wildfire smoke. Fine particulate matter found in wildfire smoke may be more toxic than equivalent doses found in ambient air.

Once inhaled, PM2.5 enters the deepest recesses of the lungs and crosses into the bloodstream, therefore poisoning other vital organs as well. Thanks to environmental regulations, over the past decades, PM2.5 levels in the US have decreased except in regions affected by wildfires. Nevertheless, experts predict that levels will rise with climate change.2

The Air Quality Index (AQI) is used by government agencies to relay the status of air quality in an area, information on who is affected, and steps taken to reduce exposure. This measure recapitulates the most common ambient air pollutants that are regulated via the Clean Air Act, including ozone and particle pollution (PM10 and PM2.5).3

The AQI takes aim at symptoms from wildfire exposure that can occur within hours or days of exposure to polluted air. It employs a scale from 0 to 500, with levels above 100 considered unhealthy first for most vulnerable populations, and as levels rise, for the whole population. During the current wildfire season, a large swathe of land blanketing Ontario and New York registered as code red, or unhealthy for all persons (ie, AQI of 151-200).4

It should be noted that it’s still unclear whether the toxic impact of wildfire smoke is diluted when it travels hundreds or thousands of miles from its source. “This is a much-needed area of research,” said pulmonologist R. Sharon Chinthrajah, MD, associate professor of medicine and of pediatrics at Stanford School of Medicine in California, in an interview.

“The toxic effects of wildfires differ depending on the source material for the fire, so fires in nearby areas could have a different toxicity profile than wildfires in different climates,” Dr Chinthrajah noted. “However, for practical purposes, it is best to consider wildfire smoke as just wildfire smoke: it is harmful regardless of where it comes from or how far it’s traveled. It is important to consider that wildfires not only increase the particulate matter in the air, but that wildfire smoke also contains additional toxic compounds that can exacerbate underlying disease.”

Lung and Systemic Effects

In an exclusive interview, Nitin Bhatt, MD, pulmonologist at the Ohio State University in Columbus, commented on the short- and long-term impacts of the inhalation of wildfire smoke.

“Symptoms most often noted in the short-term exposure to wildfire smoke are allergic and respiratory symptoms related to increased inflammation from the particulate matter,” said Dr Bhatt, who is also chair of the Occupational & Environmental Health Section of the Diffuse Lung Disease Network with the American College of Chest Physicians.

Wildfire smoke exposure symptoms include:

  • Watery/itchy eyes
  • Corneal abrasions5
  • Sinus/nasal congestion and drainage
  • Headaches
  • Increased shortness of breath
  • Dyspnea on exertion
  • Chest tightness/bronchospasm
  • Wheezing
  • New/increased sputum production

Wildfire smoke can also exacerbate baseline comorbidities, including chronic obstructive pulmonary disease (COPD), asthma, coronary artery disease, and strokes, as well as heart disease such as heart failure. Overall, chronic pulmonary and cardiovascular diseases are most affected.

“Longer term symptoms are less well characterized as this depends on duration of exposure, degree of exposure, type/composition of particulate matter in the smoke, and underlying health of the patient. Generally, this is thought to include more difficulty in control of chronic health conditions such as asthma, COPD, cardiovascular disease. Patients may report new or worsened allergic or asthma symptoms,” Dr Bhatt explained.

Of additional concern to all clinicians, exposure to wildfire smoke also predicts mental illness, as explained in a review published in the New England Journal of Medicine.

“Owing to traumatic experiences, property loss, and displacement, residents in areas affected by wildfires are at an increased risk for mental illness, including post-traumatic stress disorder, depression, and insomnia. The psychological consequences of wildfire events can persist for years, and children and adolescents are particularly vulnerable,” the authors wrote.

Managing Wildfire Exposure

Pulmonologists, in particular, should be on alert during wildfire season and assess their patients accordingly.

“I believe that providers/physicians should assess any patient to determine if effects from environmental exposure are acutely aggravating an underlying respiratory condition and take immediate steps to assess the degree and persistence,” said Richard Barbers, MD, FCCP, pulmonologist at the University of Southern California, Los Angeles, and Chair of the Asthma & COPD Section within the Airways Disorders Network with the American College of Chest Physicians, in an exclusive interview.

“If clinical circumstances dictate, then the advice would be to limit exposure, treat with appropriate interventions especially for patients with severe exacerbations, like frequent assessments, closer monitoring or even in-hospital monitoring and needed therapy,” he added.

Steps to decrease exposure in patients with COPD, asthma, or both can include wearing masks; restricting outdoor activities; and closing windows, doors, and so forth to keep the outside air out. If these measures fail to relieve exacerbated symptoms, prompt medical attention is necessary.

Dr Bhatt echoed these insights. “Follow up would depend on the nature and chronicity of a patient’s symptoms. Generally, the acute exacerbations tend to be short-lived for most patients. If patients do not return to their baseline level of symptoms severity or symptom control, they may require further evaluation.”

He also warned of the insidious nature of exposure. “Be aware of potential exposures as a cause of a patient’s symptoms, as symptoms may not develop until several days later and many areas currently being exposed to wildfire smoke have not had significant exposures recently. Counsel patients on avoiding or minimizing exposures such as staying indoors [and the] use of masks. Encourage appropriate use of medications [and] inhalers to help manage their underlying diseases.”

Dr Chinthrajah further delved into the benefits of masks based on her experience as a West-Coast pulmonologist used to dealing with wildfire exposure in patients.

“In particularly bad areas it would be helpful to use a HEPA filter,” she said. “N95 masks can help protect against particulate matter in the air when you need to go outside, however these masks do not protect against hazardous gases such as carbon monoxide, formaldehyde, and acrolein. It is important to keep in mind that these masks can run out very quickly in stores during wildfires, so it is a good idea for especially vulnerable patients, such as those with asthma to prepare ahead of time. Also note that N95 masks are not made to fit children,” she stated.

Learning More About Exposure

The EPA offers a Wildfire Smoke Course for continuing medical education credit (CME) for clinicians who want to review important points on the health effects of wildfire exposure. Some important points covered by the course include strategies at-risk patients can take to limit exposure, how to use the AQI to counsel patients, and tips on interprofessional collaboration to decrease risk.6


  1. Canada.ca. Wildfire smoke, air quality and your health. Updated and accessed June 30, 2023.
  2. Aguilera R, Corringham T, Gershunov A, Benmarhnia T. Wildfire smoke impacts respiratory health more than fine particles from other sources: observational evidence from Southern CaliforniaNat Commun. 2021;12(1):1493. doi:10.1038/s41467-021-21708-0
  3. EPA.gov. Wildfire Smoke and Your Patients’ Health: The Air Quality Index. Accessed June 30, 2023.
  4. EPA.gov. AirNow Interactive Map of Air Quality. Accessed June 30, 2023.
  5. Xu R, Yu P, Abramson MJ, Johnston FH, Samet JM, Bell ML, Haines A, Ebi KL, Li S, Guo Y. Wildfires, Global Climate Change, and Human Health. N Engl J Med. 2020;383(22):2173-2181. doi:10.1056/NEJMsr2028985
  6. EPA.gov. About the Wildfire Smoke Course. Accessed June 30, 2023.

This article originally appeared on Pulmonology Advisor