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Wildfires that burn homes and vehicles could expose people to dangerous airborne compounds through ash and smoke. Research published in ACS ES&T Air has shown that people returning to their unburned homes may also experience health symptoms months after a nearby fire is extinguished. Through a survey of people affected by the 2021 Marshall Fire in Boulder, Colorado, researchers found that headaches, sore throats and coughs were frequently self-reported by residents living near burned structures.
Wildland-urban interface fires, like the Marshall Fire and the fires in early 2025 across Los Angeles, burn both natural vegetation and human-made materials. Polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) are emitted at higher levels from human-made materials than natural biomass when burned. Exposure to these airborne compounds has been linked to negative health outcomes, including lung and cardiovascular diseases, according to the World Health Organization. After the Marshall Fire, researchers from the nearby University of Colorado, Boulder, found elevated levels of PAHs and VOCs in unburnt homes damaged by smoke, but they didn’t investigate what negative health outcomes might have been caused by exposure to these compounds. So, another CU Boulder team, led by Colleen Reid, designed and launched a survey to understand the potential symptoms experienced by residents.
The survey was conducted twice, once at 6 months after the fire (642 respondents) and again at 1 year (413 respondents), among participants whose homes remained intact. The researchers asked participants about post-fire smoke impacts and health symptoms. They found that:
- The most common fire-related symptoms were itchy or watery eyes, headaches, dry coughs, sneezing and sore throats.
- 61% of respondents reported campfire- or chemical-like smells in their homes 1 week after the fire, but those smells dissipated over time.
- 65% of respondents reported ash in their homes post-fire.
- Most respondents were less confident in the air quality of their home and neighborhood 6 months post-fire than pre-fire, but most of that confidence was restored by the 1-year mark.
The team found that many self-reported symptoms (headaches, strange taste in the mouth) clustered together for residents whose homes were within 250 meters of a burned structure. In addition, dry coughs, itchy/watery eyes and sneezing were statistically associated with a change in the home’s smell post-fire and/or finding smoke damage or ash inside. In fact, respondents who found visible ash in their home were over three times more likely to report headaches than people who didn’t. Many participants said that cleaning their homes or HVAC systems, hiring cleaning companies, or replacing affected furniture or carpets helped reduce the smell over time. Researchers hope their findings will inform future regulations and guidelines on how to return home safely after a wildfire.
The authors acknowledge funding from the National Science Foundation, the Cooperative Institute for Research in Environmental Sciences (CIRES) Rapid Innovation Research Program at the University of Colorado, Boulder, the Harvard JPB Environmental Health Fellowship, and the Developmental Core of the University of Colorado Population Center.