Thick haze from hundreds of wildfires burning across Canada has blanketed much of the Midwest and Northeast this week, triggering air quality alerts in 19 states and exposing more than 120 million people to dangerous levels of fine particulate matter.
Air quality has deteriorated sharply.
Wildfire Smoke Shows Higher Toxicity Than Typical Pollution
Researchers note that the fine particles in wildfire smoke, known as PM2.5, can rise sharply within hours of a fire igniting. A 2025 review in BMJ Oncology found that wildfire PM2.5 often contains 5 % to 20 % elemental carbon and at least 50 % organic carbon. Those organic compounds, created during the combustion of biomass, generate more free radicals than the background particulate matter most people encounter daily.
Free radicals are linked to inflammation and oxidative stress in the lungs, making the smoke more harmful per unit of exposure. The review stresses that this composition difference means a given dose of wildfire smoke can be more toxic than the same dose of usual ambient air pollution.
Link Between Smoke Exposure and Cancer Rates
Components of wildfire smoke, including certain polycyclic aromatic hydrocarbons, are already recognized as carcinogenic. While the International Agency for Research on Cancer has not formally classified wildfire smoke as a Group 1 carcinogen, studies suggest a connection to higher cancer incidence.
A large observational cohort that followed 2 million Canadians for a median of 20 years found that people living within 50 kilometers of a wildfire in the past decade experienced a 4.9 % relative increase in lung cancer and a 10 % relative increase in brain cancer compared with unexposed groups.
For cancer patients recovering from lung cancer surgery, the data are especially concerning. Those exposed to wildfire smoke in the first three months after their operation faced a 43 % higher risk of death than peers without such exposure. The risk was 39 % for exposures between four and six months post‑surgery and 17 % for exposures between seven and twelve months.
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Smoke Travels Far, Affecting Distant Communities
One detail that often surprises people is that wildfire smoke can travel thousands of miles. The same BMJ Oncology review notes that smoke from fires on the West Coast of the United States or Canada can reach the East Coast. This week, fires in Ontario have sent haze across New York City, New Jersey and much of the Northeast, illustrating how distant fires can impact air quality far from their source.
Wildfire smoke events are becoming more frequent and more intense as rising temperatures, prolonged droughts and longer fire seasons create conditions for larger and more destructive fires. The compounds found in smoke generate a greater potential for inflammation and oxidative stress in the lungs compared with everyday air pollution.
People with lung cancer or those who have undergone thoracic surgery should consider talking to their oncologist about extra precautions during active smoke events. Regularly checking local air quality index levels and limiting outdoor time when smoke is heavy are practical first steps.
In practice, this means staying indoors with filtered air when the AQI climbs above the “unhealthy” threshold, which can be a daily reality during peak fire season.
While the immediate health impacts are clear, the long‑term implications for survivorship remain less certain. Ongoing research will need to clarify whether repeated smoke exposure could affect cancer recurrence rates or overall survival beyond the acute risks noted in recent studies.
Authorities continue to monitor air quality and issue alerts as conditions evolve. Residents in affected areas are urged to follow official guidance and consider personal protective measures, such as using N95 respirators when exposure cannot be avoided. The situation shows how climate‑driven fire activity can intersect with public health, particularly for vulnerable populations.
