Health Effects Attributed to Wildfire Smoke
This section of the course covers the following topics:
• Health Effects from Smoke and the Scientific Evidence
• Durations of Smoke Exposure
• Symptoms of Mental Health Effects from Smoke Exposure
Health Effects from Smoke and the Scientific Evidence
There is a large and extensive scientific evidence base demonstrating a relationship between numerous adverse health effects and short-term (i.e., daily or 24-hour average over one or more days) ambient PM2.5 exposures including respiratory- and cardiovascular-related morbidity and pre-mature mortality (U.S. EPA 2019; U.S. EPA 2022). Studies focusing on short-term wildfire smoke exposures report evidence of health effects consistent with those observed with short-term ambient PM2.5 exposures (Liu et al. 2015; Reid et al. 2016; Cascio et al. 2018). The results are particularly consistent with respiratory-related effects, with fewer studies reporting generally consistent results for cardiovascular-related effects (U.S. EPA 2019; U.S. EPA 2022). For example, as shown in Figure 4, there is evidence of an increase in the risk of both cardiovascular- and respiratory-related ED visits as the density of wildfire smoke increases (Wettstein et al. 2018).
density and cardiovascular, cerebrovascular and respiratory ED visits across age ranges in California, 2015.
Source: Wettstein et al. (2018)
The health effects of short-term PM2.5 exposure, and subsequently smoke, can range from relatively minor (e.g., eye and respiratory tract irritation) to more serious health effects (e.g., exacerbation of asthma and heart failure and premature death) (Table 1). In addition, there is initial evidence that short-term smoke exposure may lead to preterm birth (Picciotto et al. 2024) and impact brain function (i.e., cognitive performance as measured through a brain-training game) (Cleland et al. 2022). Fine particles are respiratory irritants, and exposures to high concentrations can lead to persistent coughing, phlegm, wheezing and difficulty breathing. Exposure to PM2.5 may affect the body’s ability to remove inhaled foreign materials, such as viruses and bacteria, from the lungs. For example, some studies have reported an increase in the risk of COVID-19 cases and deaths in response to wildfire smoke exposure (Zhou et al. 2021; Meo et al. 2021; Schwarz et al. 2022). Although most healthy people will recover quickly from smoke exposure, some may experience health effects such as pulmonary inflammation and transient reductions in lung function (U.S. EPA 2019).
Ozone concentrations may also be elevated during wildfire smoke events, but downwind of fires where smoke is less dense and atmospheric conditions are conducive to its formation. Elevated ozone concentrations can lead to a range of respiratory effects such as reductions in lung function, inflammation of the airways, chest pain, coughing, wheezing and shortness of breath – even in healthy people. These effects can be more serious in people with asthma and other lung diseases. Children, older adults and outdoor workers are also at increased risk of experiencing ozone-related health effects (U.S. EPA 2020). There is also limited evidence indicating associations between ozone exposure and other health outcomes, such as cardiovascular effects and premature mortality (U.S. EPA 2020). You can learn more about ozone in EPA’s Ozone and Your Patients’ Health course.