Research Summary

Wildfire Smoke Exposure Linked to More Migraine and Headache ED Visits

Ashton L. Stahl

Key Highlights

  • The study included 997,701 emergency department visits in Alberta and Ontario.
  • Each 5-μg/m³ increase in wildfire-sourced PM2.5 was associated with a 6.07% increase in headache-related visits.
  • PM2.5 concentrations on non-wildfire days were not significantly associated with emergency department visits.
  • Associations varied across material and social deprivation levels but did not follow a monotonic pattern.

Acute exposure to wildfire-sourced fine particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) was associated with increased emergency department (ED) visits for migraine and other primary headache syndromes in 2 Canadian provinces, according to findings published in JAMA Network Open. The magnitude of the association was greater for wildfire-sourced PM2.5 than for PM2.5 recorded on non-wildfire days.

Researchers conducted a time-stratified case-crossover study of ED visits in Alberta and Ontario during wildfire seasons, defined as May 1 through October 31, from 2010 to 2023. Case days were matched with referent days by day of the week, month, year, and forward sortation area. Wildfire-sourced PM2.5 exposure was estimated using the Canadian Optimized Statistical Smoke Exposure Model, and conditional logistic regression models were used to evaluate cumulative exposure lags from 0 to 7 days. Models were adjusted for temperature and relative humidity.

Study Findings

The analysis included 997,701 ED visits among 622,753 patients with a mean age of 24.6 years; 76.3% of visits involved female patients. Migraine accounted for 86.2% of visits, while other primary headache syndromes accounted for 13.8%. Overall, 4.7% of visits occurred on wildfire days.

For every 5-μg/m³ increase in wildfire-sourced PM2.5, ED visits for migraine and other primary headache syndromes increased by 6.07% (95% CI, 5.75%-6.39%) across both provinces. The corresponding increases were 6.45% (95% CI, 5.89%-7.02%) in Alberta and 5.89% (95% CI, 5.52%-6.27%) in Ontario. By comparison, PM2.5 on non-wildfire days was not significantly associated with ED visits (0.21%; 95% CI, −0.20% to 0.62%).

Associations varied by material and social deprivation. The smallest increase occurred in the least-deprived quintile at 3.61% (95% CI, 1.93%-5.30%), while the largest occurred in the most-deprived quintile at 10.42% (95% CI, 7.41%-13.49%). However, the pattern was nonmonotonic and differed between provinces.

Clinical Implications

According to the study authors, the findings suggest wildfire-sourced PM2.5 may precede severe headache episodes requiring ED care. They stated that additional research into wildfire smoke and severe headache-related outcomes is needed, including research examining potential mediating pathways and smoke-exposure interventions.

The researchers lacked information about preexisting headache diagnoses and medication use. They also could not measure indoor or personal wildfire-smoke exposure or isolate the effects of particulate matter from other pollutants emitted by wildfires.

Expert Commentary

“In this case-crossover study of ED visits in Alberta and Ontario, acute exposure to wildfire-sourced PM2.5 was associated with increased ED visit for MOPHS; associations were greater in magnitude for wildfire-sourced PM2.5 than nonwildfire-sourced PM2.5. These findings support the need for further research into wildfire smoke and severe headache–related outcomes,” the researchers concluded.

Reference

Dales R, Paul N, Cleland SE, et al. Wildfire-sourced PM2.5 and emergency department visits for migraine and other primary headache. JAMA Netw Open. 2026;9(7):e2625015. doi:10.1001/jamanetworkopen.2026.25015