When wildfires rage, the first and most visible impact is on air quality. Thick, smoky skies push people indoors to avoid breathing in the hazardous particles. But a new study warns that this very move—to stay safe from smoke—could make people more vulnerable to contagious respiratory illnesses like influenza and COVID-19.The findings, published in PLOS Climate by researchers from Georgetown University, suggest that increased indoor crowding during wildfire events could create the perfect storm for airborne viruses to spread more easily.What the Study Looked AtTo understand this link, researchers used anonymized mobile phone data tracking visits to more than 4.6 million locations across the United States—ranging from parks and trails to malls and restaurants. They focused particularly on the 2020 wildfire season in Oregon and Washington, when large-scale fires blanketed the states in thick smoke between July and November.Air quality data helped identify the counties hit hardest. The researchers then compared changes in people’s movements before, during, and after the wildfires.People Headed Indoors—and Stayed ThereThe analysis showed a clear shift: as the wildfires worsened, people sought refuge indoors.In Oregon, indoor activity jumped by 14%.In Washington, it rose by nearly 11%.Major cities like Seattle and Portland saw even bigger increases—16% and 11%, respectively.More time indoors means more shared air—and a greater chance for viruses to spread among those sharing that space.Why This Matters for Flu and COVID-19Respiratory viruses like the flu and COVID-19 thrive in enclosed environments, especially where ventilation is poor and people are in close contact. The researchers used computer models to estimate the likely increase in infection rates caused by this behavioral shift.Their findings? Crowded indoor spaces during wildfire events could significantly boost peak infection numbers—unless precautionary measures are taken.Masking Can Make a DifferenceFortunately, there’s a simple step that could help counter this risk: mask-wearing indoors.“Even a modest increase in mask use—just 10%—can help reduce the peak of infection during wildfires,” the researchers wrote. In some places, like Washington County in Oregon or Yakima County in Washington, more robust measures (over 50% masking rates) may be needed to truly reduce transmission.Planning Ahead for a Warming WorldAs wildfires become more frequent and intense due to climate change, public health officials must start thinking ahead—not just about air quality but also about how people behave in response.“Our study shows that emergencies like wildfires don’t just affect the environment—they also change how we live day to day,” said lead researcher Giulia Pullano, a postdoctoral fellow in epidemiology. “If we understand that, we can prepare better.”In short: what protects us from wildfire smoke might leave us exposed to something else. But with awareness and action, communities can stay safe on both fronts.