When wildfires began racing through the Los Angeles area on Jan. 7, 2025, the scope of the disaster caught residents by surprise. Forecasters had warned about high winds and exceptionally dry conditions, but few people expected to see smoke and fires for weeks in one of America’s largest metro areas.

Environmental health scientist Yifang Zhu studies air quality at UCLA and began collecting samples from inside and outside homes the day after the fires began. In this Q&A, she describes findings by her team, a consortium of universities and local projects, that are painting a picture of the health risks millions of Los Angeles-area residents faced.

Their research offers both a warning and steps people everywhere can take to protect their homes and themselves from wildfire smoke in the future.

Urban fires are unique in a sense that it’s not just trees and other biomass burning. When homes and vehicles catch fire, plastics, electronics, cleaning chemicals, paints, textiles, construction material and much more burns, releasing chemicals and metals into the air.

More than 16,000 buildings burned in LA. Electric vehicles burned. A dental clinic burned. All of this gets mixed into the smoke in complicated ways, creating complex mixtures that can have definite health risks.

One thing we’ve found that is especially important for people to understand is that the concentration of these chemicals and metals can actually be higher inside homes compared with outside after a........

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