Reza Ronaghi lost his home in the Los Angeles wildfires last week.
"Not a single house survived in our two-block area," he said.
Ronaghi is a pulmonologist at the University of California, Los Angeles. So he is well-acquainted with the health risks associated with breathing in wildfire smoke. But even he, a medical professional, was shocked to see how many potential health risks lurked in the detritus, ash, and smoke left behind after the fires.
"This is not just a regular fire," he said. "Thousands of houses and all the material the house was made of, the inside, the appliances, the roof, the list goes on."
But what alarmed him more was how little health and safety guidance officials offered to residents returning to the neighborhood to see what was left of their homes.
He and several neighbors were allowed back into their Pacific Palisades neighborhood a few days after the burn: the ground was still smoking. He wore an N95 mask, but quickly realized he should have more thoroughly protected himself—with gloves, goggles, a respirator mask like those used when working with chemicals, and long clothes that he could remove and bag immediately after leaving the area.
After just 20 or 30 minutes, he said, his eyes were watering and his nose was irritated. Later on, he realized his skin was irritated where it had accidentally been exposed to debris and polluted air.
Previous scientific research shows that the detritus left behind after a fire can be laden with toxic compounds and gases, from heavy metals to burned plastics to asbestos. Exposure to the ash and even air can cause short-term health impacts, from the runny eyes Ronaghi experienced to respiratory issues and more.
But it's not just the immediate health issues that concern Ronaghi. The exposure people experience now, he worries, could lead to health effects down the road.
Exposure to toxic materials left behind after houses burn can be "actually much more dangerous than what smoke may do to your lungs alone," he says.
So as people return to their homes, he wants them to take care—because "right now, we're talking about long-term consequences."
It matters what materials have burned
Wildfire smoke and ash can be dangerous to people's health even when a fire primarily burns trees and plants. But fires that burn through man-made materials are often filled with a more toxic mix. After California's 2018 Camp Fire, researchers found abnormally high concentrations of lead downwind of the burn, which they suspect came from the houses that went up in smoke. Researchers in Los Angeles have found preliminary suggestions that the ash there has high concentrations of metals, as well. Exposure to lead can lead to short-term problems like headaches or dizziness. High exposures have been associated with issues from cognitive trouble to reproductive and cardiovascular problems.
It's not just metals. Appliances, coolant fluid, polyester curtains, cleaning products—all the manmade parts of a house can produce a rich suite of health-harming compounds and gases, like benzene and formaldehyde, and polycyclic aromatic hydrocarbons, or PAHs.
But research on the long-term effects of wildfire smoke has only recently begun. Surveys after the Lahaina wildfires in 2023 found that residents exposed to smoke and ash experienced increases in heart, kidney, and mental health issues. An EPA-led study exposed mice to smoke from army burn pits, which include many materials that might be found in burning homes and cars; the mice exposed to the smoke showed signs of inflammation and lung injury.
In the most damaged and contaminated areas, officials will usually send in debris-removal teams to clear away the most dangerous waste and ash. But Ronaghi stresses that anyone visiting the area before that process is complete should take precautions.
He recommends anyone visiting sites that burned use N95 masks or respirators, if possible, along with goggles to protect their eyes (ski or swim goggles would work in a pinch, he says); gloves; and long clothes that they can remove before going back to wherever they're staying. Bag those clothes during transport, and wash them immediately upon arriving home, other experts suggest, to avoid bringing hazards into your living space.
Even those whose homes are still standing, including those far from the front lines of the fire, may be contending with ash and smoke. Research conducted after the 2021 Marshall Fire in Boulder, Colo., found that "smoke managed to penetrate indoors and through cracks underneath doors and windows," in homes downwind of the fire, says Joost de Gouw, a University of Colorado, Boulder atmospheric chemist and author of one of the studies. Residents reported health disturbances, from headaches to respiratory problems, for weeks afterward.
After the Marshall Fire, hazardous gases associated with the wildfire smoke, such as benzene and naphthalene, could be detected in homes downwind of the fire long after the burns were put out. Those gases, another study suggested, could have been absorbed by textiles, mattresses, and maybe even the wood framing and drywall in homes.
Those gases take time to dissipate, de Gouw says, during which period residents may still be exposed.
After the fire, "all of these gases that were absorbed into building materials were slowly being rereleased through indoor air, where you were smelling them," he says. "That process took about five weeks before everything ventilated out again."
How to clean up
Even for those farther from the burned neighborhoods, the cleanup could be dangerous—and could stretch over weeks.
Because the leftover ash and smoke can contain dangerous components, experts who spoke with NPR recommend protecting yourself thoroughly whenever you clean your home if it was affected by wildfire smoke.
"People who are going back to these homes should wear N95 masks to protect themselves," says Colleen Reid, a health geographer at the University of Colorado, Boulder, who worked on one of the Marshall Fire smoke studies. "We found that when people cleaned, it resuspended that ash," lifting it back into the air where people might inhale it.
Reid also suggests wearing gloves and long-sleeved clothes and pants while cleaning.
She says scientists are still working on coming up with rigorously tested recommendations for best cleaning practices after wildfires. But a 2023 study shows that cleaning a home's hard surfaces by dusting, wiping down with damp cloths, and mopping can effectively lower the concentrations of smoke-associated gases.
Reid suggests "using a HEPA-filter vacuum, and really cleaning all the surfaces—like wiping them down to try to remove those sources of the chemicals that are off-gassing."
More porous surfaces, like couches and other textiles, can persist as an ongoing source of exposure; Reid suggests replacing them, if possible.
de Gouw and other researchers found that constantly running air filters with activated carbon lowered the gas concentrations in those first weeks after the fire. But concentrations went back up when the air filters were stopped—so "it's important to keep them running for those few weeks," he says.
Research from Portland State University found that PAH levels can be lowered post-fire by simple cleaning and washing any textiles that can be washed. Long-term exposure to PAH's has been linked to increased risk of cancer.
The message, says de Gouw, is to clean everything one can carefully and thoroughly, because the smoke can affect nearly every part of a home—even in houses far from the fire line. Any efforts to lower the dose of potentially dangerous smoke and ash byproducts can help protect people, he says.
Ronaghi is still dealing with the fallout of the fires. For now, his family is dealing with the loss of their home and figuring out how, and where, to rebuild their life.
But as he processes, he wants to make sure others understand the ongoing risks.
"Most of the time we hear about fires and we say, okay, you know, we'll be okay. We're kind of removed from it," he says. But for people across Los Angeles right now, it's all too possible to be exposed to health-damaging toxins right now. "And you won't know for a very, very, very long time," he says. "And so that's why it's super important" to protect yourself.
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