How to keep the air inside your home clean during wildfires

The sun is obscured by wildfire smoke as a person runs in front of the Washington-monument" class="entity-link entity-location" data-entity-id="22460" data-entity-type="location">Washington Monument and Lincoln Memorial Reflecting Pool, Friday, July 17, 2026, on the National Mall in Washington. (AP Photo/Julia Demaree Nikhinson) By Devi Shastri Updated 12:17 AM MESZ, July 20, 2026 Leer en español Add AP News on Google Add AP News as your preferred source to see more of our stories on Google. Share Share Facebook Copy Link copied Print Email X LinkedIn Bluesky Flipboard Pinterest Reddit MILWAUKEE (AP) — The eerie glow of an orange sun through thick wildfire smoke might be unnerving, but the biggest risk from the haze is something much harder to see. Tiny particles in the air can cause a range of short-term and chronic health issues, experts say. Wildfire smoke can settle over cities for days — like the recent blanket over parts of the U.S. from burning fires in Canada, which has created hazardous air for millions of people across multiple states. Health officials advise people to stay indoors — and to take steps to keep the air in your home clean. undefined AP AUDIO: How to keep the air inside your home clean during wildfires Health experts say the biggest risk from distant wildfires is something that’s much harder to see. AP correspondent Donna Warder has this special report. If you have central air conditioning, it should clean the air in your home. Make sure filters are replaced on schedule and are of the highest level of filtration your system can handle. Filters rated MERV 13 or higher are ideal. Set the air to recirculate and close any vents that pull air from outside if you can. The University of Oregon’s Center for Wildfire Smoke Research and Practice recommends running the system’s fan through the entire smoke event, not just when cooling. If you can only afford one portable air filter, use it to create a “clean room” in your house where you can spend most of your time. “The basic message is that something is better than nothing,” said Amy Kalkbrenner, an environmental epidemiologist at the University of Wisconsin-Milwaukee. There’s good evidence that DIY filters made by duct-taping furnace air filters to a box fan work. They’re simple, relatively affordable and scientists at the Environmental Protection Agency have found they are just as good at removing fine particles of pollution from the air as a small commercial air purifier. More from Be Well Autoimmune diseases can strike any part of the body, and mostly affect women. Here’s what to know 13 Calisthenics are making a comeback. Is body weight enough to get a good workout? 24 Gut microbiome tests are everywhere. Should you get one? 12 “The good news is they really work,” said Kalkbrenner. All you need to have to make one is: four 20-by-20-inch (50.8-by-50.8-centimeters) furnace air filters rated MERV 13 or higher, a box fan, cardboard and duct tape. The EPA’s website shows how you can modify the design to only use one or two filters. The fan should blow out, and the arrows on the filters should point in. Make sure everything is taped up airtight. Many window air conditioners, mini-split heat exchangers and portable air conditioners don’t have the filters needed to remove fine pollution particles. But heat can also be dangerous. “When smoke and heat occur together, the impacts on your health are even greater than when they occur by themselves,” said Jess Downey, a researcher at the University of Oregon’s Center for Wildfire Smoke Research and Practice Downey said the ideal scenario is running the AC unit and using an air purifier or a DIY box fan filter to clean the air. Make sure your AC is well-sealed in your window frame, she added. Make sure the window units are set to recirculate air. Portable units with a single hose should be used sparingly, according to the University of Oregon wildfire smoke center. If you don’t have AC, any reprieve from hot, smoky air is important. Head to the library, shopping mall or other space with clean, cool air. Whether it’s a towel, some tape, or something else — plug areas where air could enter from outside. “Being from Chicago, I think you can liken it to trying to keep the cold air out,” said Dr. Khalilah Gates, a lung doctor with Northwestern Medicine. “Any areas in which air can come in, consider sealing up those areas to reduce the amount that’s coming into the home.” When smoke levels are high, experts recommend avoiding anything that burns — candles, fireplaces, even gas stoves — so plan ahead with some meal prep. Exposure to wildfire smoke can lead to shortness of breath, chest tightness, headaches, and a burning sensation in the nose and eyes. “When you ever start to feel those symptoms and they’re not severe, it’s important to acknowledge, ‘Oh, my body is responding to this. I need to move away from it. I need to move inside,’” Gates said. If you’re wheezing, can’t catch your breath or are in distress, get to the emergency room immediately, she said. The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content. Devi Shastri Shastri is a public health reporter for The Associated Press, based in Milwaukee. She covers housing access, the social safety net, medical misinformation and other topics that influence the health of communities broadly. twitter mailto