When wildfires spread into neighborhoods, they burn all kinds of materials found in cars and houses and everything around them – electronics, paint, plastics, furniture.

Research shows that the mix of chemicals released when human-made materials like these burn is different from what is emitted during a vegetation fire and is potentially more toxic. The smoke and ash can blow under doors and around windows in nearby homes, bringing in chemicals that are absorbed into furniture, walls and other indoor surfaces and continue off-gassing for weeks to months.

As people return to smoke-damaged homes after a wildfire, there are several steps they can take to protect their health before starting to clean.

In 2021, after the Marshall Fire swept through neighborhoods near Boulder, Colorado, my colleagues and I at Colorado universities and labs heard from many residents who were worried about the ash and lingering smells inside their homes that had otherwise survived the flames.

In homes that my colleagues were able to quickly test, they found elevated levels of metals and PAHs – polycyclic aromatic hydrocarbons – in the ash. We also found elevated VOCs – volatile organic compounds – in airborne samples. Some VOCs, such as dioxins, benzene, formaldehyde and PAHs, can be toxic to humans. Benzene is a known carcinogen.

At the time, we could find no information about physical health implications for people who have returned to smoke-damaged homes after a wildfire. So, to look for patterns, we surveyed residents affected by the fire six months, one year and two years after the fire.

Even six months after the fire, we found that many people were reporting symptoms that aligned with health risks related to smoke and ash from fires.

More than half (55%) reported that they were experiencing at least one symptom six months after the blaze that they attributed to the Marshall Fire. The most common symptoms reported were itchy or watery eyes (33%), headache (30%), dry cough (27%), sneezing (26%) and sore throat (23%).

All of these symptoms, as well as having a strange taste in one’s mouth, were associated with people reporting that their home smelled differently when they returned to it one week after the fire.

Many survey respondents said that the smells decreased over time. Most attributed the improvement in smell to the passage of time, cleaning surfaces and air ducts, replacing furnace filters, and removing carpet, textiles and furniture from the home. Despite this, many still had symptoms.

We also found that living near a large number of burned structures was associated with these health symptoms. We found that for every 10 additional destroyed buildings within 820 feet (250 meters) of a person’s home, there was an associated 21% increase in headaches and a 26% increase in having a strange taste in their mouth.

These symptoms align with what could be expected from exposure to the chemicals that we found in the ash and measured in the air inside the few smoke-damaged homes that we were able to study in depth.

There are a still a lot of unanswered questions about the health risks from smoke- and ash-damaged homes.

For example, we don’t yet know what long-term health implications might look like for people living with lingering gases from wildfire smoke and ash in a home. We found a significant decline in the number of people reporting symptoms one year after the fire. However, 33% percent of the people whose homes were affected and responded to a later survey still reported at least one symptom that they attributed to the fire. About the same percentage also reported at least one symptom two years after the fire.

We also could not measure the level of VOCs or metals that each person was exposed to. But we do think that reports of a change in the smell of a person’s home one week after the fire demonstrates the likely presence of VOCs in the home. That likely has health implications for people whose homes are exposed to smoke or ash from a wildfire.

Wildfires are increasingly burning homes and other structures as more people move into the wildland-urban interface, temperatures rise and fire seasons lengthen.

If your home survives a wildfire nearby, here are some of the steps to think about before starting to clean:

When you’re ready to clean your home, start by protecting yourself. Wear at least an N95 (or KN95) mask and gloves, goggles and clothing that covers your skin. Cleaning can send some of those gases and ash into the air again.

Keep people with heart or lung diseases, older adults, pregnant women, children and pets away from cleanup activities.

Vacuum floors, drapes and furniture. A recent scientific study documents how cleaning all surfaces within a home can reduce reservoirs of VOCs and lower indoor air concentrations of VOCs. Once the air outside has cleared, open windows to let clean air in.

Avoid harsh chemical cleaners because they can react with the chemicals in the ash.

Clean your HVAC filter and ducts to avoid spreading ash further, and change filters monthly until the smell is gone. Portable air cleaners with carbon filters can help remove VOCs and particles.

If your car smells of smoke, consider changing the cabin air filter.

This is an update to an article first published Dec. 23, 2024.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Colleen E. Reid, University of Colorado Boulder

Read more:
How Santa Ana winds fueled the deadly fires in Southern California

Wildfire smoke linked to thousands of premature deaths every year – here’s why and how to protect yourself

Wildfire smoke changes dramatically as it ages, and that matters for downwind air quality – here’s what we learned flying through smoke plumes

Colleen E. Reid receives funding for her research from the U.S. EPA, NSF, and NIH and she has received funding in the past from the CDC, the Health Effects Institute, the JPB Foundation, and the Robert Wood Johnson Foundation.