Forest fires: Assessing the health risks posed by the smoke

Smoke from forest fires is more toxic than "normal" air pollution, can remain in the air for a long time and travel very long distances.

Risks for cardiovascular patients, asthmatics and the elderly

Certain fumes contain a variety of harmful gases and particles

When carbonaceous materials are burned, the smoke from any fire (forest, bush, grain, construction, tyre, waste or wood fires) releases particulates and chemicals. All smoke contains carbon monoxide, carbon dioxide and particulate matter (also referred to as PM or soot).2

In addition to soil particles and biological material, smoke from wildfires often contains traces of chemicals, metals, plastics and other synthetic materials, because it is not only plants and trees that burn, but also residential areas and their components.1 Therefore, the smoke may contain aldehydes, acid gases, sulphur dioxide, nitrogen oxides, polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, styrene, metals and dioxins, among others. The composition of the smoke is also influenced by how much oxygen is available and how high the temperature is.2

Fine particulate matter from smoke (PM2.5) can penetrate deep into the respiratory tract and cause respiratory irritation and shortness of breath, as well as exacerbate conditions such as asthma and heart disease.2

In human studies, wildfire smoke has been linked to higher rates of myocardial infarction, stroke, cardiac arrest, a large increase in emergency admissions due to respiratory illnesses, and weakened immune defences.1 Analyses of hospital data, for example from the 2019/ 2020 Australian bushfire period, also show relevant excess mortality from cardiovascular and respiratory events.3

In the month following exposure to wildfire smoke, rates of coccidioidomycosis (respiratory infections with fungi normally found in soil) were also increased by 20%, probably due to airborne spores.4

Health effects can last for a long time

Wildfires release many carcinogenic pollutants that contaminate the air, water, soil, and indoor environments. Fittingly, data from over 2 million people followed up for a median of 20 years found that people who lived within 50 km of a wildfire in the past decade had a 4.9% increased risk of lung cancer and a 10% increased risk of brain tumours.5

After a 6-week coal mine fire in Australia that released enormous amounts of particulate matter, rates of heart disease remained elevated for 2.5 years, and emergency room visits for respiratory illness for 5 years.6

Indirectly, such events can also contribute to long-term brain changes. The deadliest and most destructive wildfire in California history was the 2018 'Camp Fire' (ignited by a faulty power line). Exposed individuals showed reduced cognitive performance and increased brain activity in the frontal brain 6 to 12 months later, likely due to stress and trauma.1,7

  1. Lapid, N. & Lapid, N. What are the health risks from wildfire smoke? Reuters (2023).
  2. Exposure to Smoke from Fires.
  3. Arriagada, N. B. et al. Unprecedented smoke‐related health burden associated with the 2019–20 bushfires in eastern Australia. Med. J. Aust. 213, (2020).
  4. Mulliken, J. S. et al. Risk of systemic fungal infections after exposure to wildfires: a population-based, retrospective study in California. The Lancet Planetary Health 7, e381–e386 (2023).
  5. Korsiak, J. et al. Long-term exposure to wildfires and cancer incidence in Canada: a population-based observational cohort study. The Lancet Planetary Health 6, e400–e409 (2022).
  6. Smith, C. L. et al. Long-term impact of the 2014 Hazelwood coal mine fire on emergency department presentations in Australia. Environmental Research 223, 115440 (2023).
  7. Harris, E. Wildfire Exposure Linked to Changes in Cognition and Brain Activity. JAMA 329, 457 (2023).

    Last website checks: 17 July 2023