Wildfires Are Increasingly Urban, Bringing New Toxic Risks

Wildfires, once largely confined to remote wilderness areas, are increasingly impacting urban and suburban communities across the United States, bringing with them a new set of health risks. This shift is driven by the expanding wildland-urban interface (WUI), where residential development encroaches on areas prone to fire.

The dangers of these fires are evolving as the landscape changes. Fires in suburban neighborhoods, like those in Spokane, Washington, this summer that destroyed over 800 homes, or the Marshall Fire in Boulder, Colorado, in 2021, which razed nearly 1,000 homes, expose more people to the toxic byproducts of burning human-made materials.

The Changing Fire Frontier

The growth of the WUI has been substantial over the past three decades. The USDA Forest Service reported a 46 percent increase in houses within the WUI zone between 1990 and 2020, with approximately one-third of all U.S. homes now located in these vulnerable areas. This expansion means that more homes are directly in the path of wildfires, and when homes, vehicles, and other structures burn, the resulting smoke contains a more complex mixture of toxins than that from vegetation fires alone.

In January 2025, fires in Los Angeles County, which burned through densely populated neighborhoods and destroyed over 16,000 buildings, provided a stark example. The smoke produced contained higher concentrations of volatile organic compounds (VOCs), metals, and chemicals from burning plastics, electronics, and electric vehicle batteries. Additionally, fire-extinguishing foams and firefighting gear can release PFAS, also known as “forever chemicals,” which are linked to adverse health effects, including increased cancer risk and immune system weakening.

Researchers have found that these toxic compounds can linger indoors long after the fires have been extinguished. Studies in the aftermath of the Los Angeles fires detected elevated VOC levels inside evacuated homes for months. This means that even residents whose homes are not directly damaged by flames can still face significant health risks from the altered air quality.

Mounting Dangers Across Populations

The health implications of these urban wildfires extend beyond immediate exposure. Studies focusing on firefighters, who are repeatedly exposed to these complex smoke mixtures, are revealing potential long-term health consequences. Research examining blood samples from firefighters has indicated that smoke exposure can affect genetic expression related to tumor suppression and may be linked to increased risks of various cancers, neurodegenerative diseases, and cardiovascular conditions.

While firefighters experience more prolonged exposure, the general population living in WUI zones is also at risk. Children may face a higher incidence of asthma and respiratory problems, while adults could experience more cardiovascular incidents. The long-term effects are still being studied, but preliminary findings suggest a potential for accumulated exposure to lead to serious health issues over time.

Even after the immediate danger of the fire passes, residual toxins can persist. For instance, high levels of chromium 6, a carcinogenic metal, have been detected in cleanup zones for weeks following fires, and abnormal concentrations of heavy metals have been found miles downwind. Furthermore, toxic compounds can contaminate waterways, and damaged air filtration systems in homes can reduce protection against future airborne contaminants. As wildfire seasons continue to intensify and spread into more populated areas, understanding and mitigating these evolving health risks is becoming increasingly critical.