- Design
- Retrospective ecological cohort, distributed lag non-linear model
- Population
- US counties in the national cancer registry, 2016–2022
- Primary outcome
- Head and neck cancer incidence over 0–10-year lags
- Effect
- cRR 1.06 (1.04–1.09) per smoke day; larynx cRR 1.13 (1.07–1.19)
A US analysis linked county-level wildfire-specific PM2.5 exposure to head and neck cancer incidence in the national cancer registry from 2016 to 2022, modelling lagged effects over 10 years and adjusting for tobacco, alcohol, diet and other behaviours and demographics.
Each additional smoke-exceedance day was associated with a cumulative relative risk of 1.06 (95% CI 1.04–1.09) over 10 years, and any annual exposure with 1.41. Laryngeal cancer showed the largest association (1.13 per exceedance day), followed by oropharyngeal (1.09) and oral cavity (1.03). Associations appeared for both p16-positive and p16-negative tumours.
This is ecological — county exposure, not individual — so it cannot show that smoke causes cancer in any person. Wildfire seasons are lengthening, and seasonal crop burning creates similar smoke exposure in parts of India, though no Indian data were included.
- Consider asking about long-term smoke exposure, including occupational and seasonal, in head and neck cancer histories.
- Continue to prioritise tobacco and alcohol, which remain the dominant risks.
- Do not tell individual patients that smoke caused their cancer; this is county-level data.
- Note the strongest association was with laryngeal cancer.
Why it matters
It adds smoke from fires to the environmental exposures that may shape head and neck cancer risk.
Don't overread it
Ecological data — it shows a county-level association, not that smoke causes cancer in individuals.
The statistics, in plain English
A cumulative relative risk of 1.06 per smoke day adds up across a bad season. But exposure was measured for whole counties, so individuals with cancer may not have been the ones exposed — the classic weakness of ecological studies.
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