The Dangers That Scientists Found Inside L.A.’s Smoky Homes

After just a year, the fires that spread around Los Angeles are already the most studied urban wildfires in history. While the Palisades Fire lapped at the edge of UCLA, the Eaton Fire, on the east side of town, came dangerously close to Caltech. Even as the fires were spreading, these research powerhouses, as well as the University of Southern California, deployed sensors, scientists, and new hypotheses. Researchers around the city began collecting water, soil, and air samples; physicians started to recruit participants into long-term health studies.

Even as the researchers absorbed the reality of the damage across an area that included 20 million residents, they understood that this was a chance, one that might never exist again, to better understand the nature of these types of disasters. These particular fires offered researchers opportunities to collect samples in ways they hadn’t before been able to—“so close to the fire and so timely,” Yifang Zhu, an environmental scientist at UCLA, told me.

Some of these efforts will take years to become fully fleshed out. The Los Angeles Fire Human Exposure and Long-Term Health Study, for instance, is a multi-institution, 10-year effort to better understand the short- and long-term health impacts of the fires. A year after the fires, though, researchers have some early answers to what happens to mental and physical health after wildfires move from trees and shrubs to homes and buildings.

Not all fires are the same, and although these fires started in the hills with scrub brush, they ended up in urban areas, flaming through more than 18,000 structures. “It’s a new type of fire, because it’s an urban conflagration,” David Eisenman, a researcher at UCLA who has spent the past 25 years studying the impact of disasters on mental and physical health, told me. These fires may start in areas where wildland and urban settlements edge up against one another, but as they spread, they “mostly consume, by volume, man‑made products in megacities—that’s a real difference.” Researchers have long studied what goes into the air when trees burn in a fire, but when the fuel is homes, cars, and businesses—the stuff of people’s lives—what ends up in the air is largely unknown. The many chemicals, including asbestos and lead, in our homes can form a toxic soup. The combustion process can also create new hazards; scientists were surprised to find airborne nanoparticles of hexavalent chromium, the contaminant made famous by the movie Erin Brockovich, hanging around cleanup sites.

One surprise lesson was that the fire risk didn’t end once the smoke had dissipated. Levels of benzene spiked, then came down after about a week. But even after the outdoor air began to clear, measures of hazardous chemicals in indoor air showed signals from fire-related compounds that had infiltrated people’s homes and kept off‑gassing. While people were looking to the smoke and fire as the danger, scientists were seeing real risk lurking inside homes, as people hunkered down. “The outdoor air became cleaner, but the indoor levels went up,” Zhu said.

Smoke has been linked to increased respiratory and heart problems, so researchers were already on high alert for some issues. Still, they dug into emergency-room data from the weeks after the fire started without any assumptions about what they might find. When researchers combed through emergency diagnoses at Cedars-Sinai Medical Center for people living in fire-affected zip codes, then compared those numbers with the same period across the previous seven years, they found that respiratory illness spiked by 24 percent. They also observed a 46 percent increase in heart-attack rates. (Fine particulates from smoke can trigger inflammation and disrupt heart rhythms.) Although researchers expected to see some of these effects, the scale put into perspective just how much of a disaster the fires had been for the city’s health: “The wildfires caused just the same amount of excess respiratory illness as the worst periods of COVID,” Susan Cheng, a cardiologist and researcher at Cedars-Sinai, who led the study, told me.  

Other health problems had less clear explanations. The team found, for instance, that abnormal blood-test results in the emergency room more than doubled. Their blood sugars or protein levels or kidney-function markers were off, and unlike the cardiac and respiratory results, those numbers stayed elevated for 60 to 90 days after the fires. Cheng said it’s too early to know why, but a study last summer showed how immune cells in wildfire-exposed people had reduced function and contained heavy metals, including mercury and cadmium. “I think we’re just still kind of at the tip of the iceberg here in terms of understanding what all the downstream effects will look like,” she said.

Eisenman started thinking about the scope of this type of damage while the fire was still consuming the Palisades. When he first saw the fire, from his house, he shrugged: Fires weren’t uncommon in the Santa Monica Mountains. But that night, as he sat awake, staring at the Watch Duty app on his phone as the fire line expanded into his favorite hiking trail at Will Rogers State Historic Park, his heart sank.

“That’s when it hit me,” he said: “This is going to have an enormous effect on people beyond the homes that were being burned.” He thought of the smoke blanketing the city, but also the mental health of people who would lose their livelihoods and houses, as well as respites in nature that might provide some breathing space.

Beyond the physical-health effects, fires also leave people with more anxiety, depression, and PTSD. Preliminary data from a survey of mental health in L.A. County show higher rates of depression, anxiety, and perceived stress after one year. And researchers have come to understand that smoke itself is associated with mental-health problems, whether because it affects people’s bodies directly or because it shuts people in their homes, cutting them off from their communities, jobs, schools, and recreation. Previously, researchers had imagined the trauma of fire as the most worrying issue, Eisenman said. “But on a population level, the smoke goes much further and affects many more people.”

As climate change makes fire conditions likelier, more areas are susceptible to fires like those that scorched Los Angeles. Areas of Australia, Chile, and Greece are experiencing extended fire seasons and fires that leap from wild areas to large cities. That could make the health insights from Los Angeles vital for other cities around the world.

But that information will be vital here, too. “We know this is going to not be the last one in L.A., and L.A. won’t be the last city to have this level of megafires,” Zhu said. This city’s experience can help write the handbook for other cities and for future disasters.