Long-term exposure to wildfire smoke is an increasing health risk, although it is not well understood

Millions of people across Los Angeles are at risk of inhaling smoke from wildfires burning their homes and vehicles. Fires that occurred in January 2025 burned thousands of buildingstogether with the building materials, furniture, paints, plastics and electronics they contain.

When materials like these burn, they can release toxic chemicals that can harm people breathing downwind.

2023 smoke examination from fires at the wildland-urban interface – areas where urban neighborhoods transition into wildlands – have found that they contain a wide range of chemicals that are harmful to humans. include hydrogen chloride, polycyclic aromatic hydrocarbons, dioxins and a number of toxic organic compounds, including known carcinogens such as benzenebut also toluene, xylenes, styrene AND formaldehyde. Scientists also found metals in the smoke, including lead, chromium, cadmium and arsenic, which are known to affect several body systemssuch as the brain, liver, kidneys, skin and lungs.

The short-term effects of exposure such smoking can trigger asthma attacks and cause lung and heart problems.

But smoke can also have long-term effects, but they are less understood. as environmental toxicologist which focuses on the health effects of wildfire smoke, I, like many of my colleagues, am increasingly concerned about the effects of long-term and repeated exposure to wildfire smoke that more people are now facing.

Long-term exposure to tobacco smoke is increasing

Across the country, acreage has burned as a result of the U.S. wildfires almost doubled in each decade since 1990. This is changing the way people are exposed to wildfire smoke.

Communities were shrouded in smoke for days and weeks more and more often. In 2023, massive wildfires in Canada repeatedly spread stout smoke to many U.S. communities. Controlled burnswhich firefighters worked to clear flammable brush and reduce the severity of future fires also cause smoke to become airborne.

There is smoke from the fires now main source of PM2.5 – microscopic particulate matter that can enter the lungs – in the western United States

This increasing exposure increases the need to understand the long-term consequences of living and working in wildfire-prone areas.

Dose, duration and frequency matter

When scientists study the health risks of wildfire smoke, they typically exploit analytical methods designed to assess the health effects caused by low-level, chronic exposure to urban air pollutants – for example, car or smokestack emissions. However, these approaches do not capture the lively and intense nature of wildfire smoke.

Scientists suspect that exposure to tobacco smoke may have different consequences for people exposed to smoke inhalation of different intensities and durations. Repeated exposure to wildfire smoke can also have worsening health effects over time.

To study the long-term effects of wildfire smoke, scientists need to know how much smoke people were exposed to, for how long and how often. This is not an experiment that can be performed on humans in a laboratory, but data can be collected from communities affected by the fires.

Currently, however, this type of data collection is infrequent.

Most studies that have looked at long-term exposure, e.g impact on dementia Or pregnancythey used average exposure over years rather than detailed exposure data.

Some focused on specific events. For example, a study of residents who were exposed to smoke inhalation for six weeks during the 2017 Rice Ridge fire near Lake Seeley, Montana, found that their lung function has significantly deteriorated for at least two years after the fire. It was a forest fire, and while burning vegetation is harmful, it is generally considered to be less toxic than burning buildings.

A different approach to smoke exposure

Better understanding the long-term effects of wildfire smoke will require looking at smoke differently.

If epidemiologists begin to clearly define in their studies the adverse health effects of exposure to wildfire smoke in terms of dose, duration, and frequency, taking into account the lively and episodic nature, then toxicologists will be able to model these human experiences in animal experiments.

These experiments could improve understanding of long-term health risks and then assist scientists develop effective guidelines and strategies to reduce harmful exposures.