As wildfires continue to produce hazardous smoke affecting large regions, health experts emphasize measures to maintain clean indoor air and reduce exposure to harmful particles. Recent smoke from fires in Canada has blanketed parts of the United States, creating unhealthy conditions for millions over several days.

The primary health risk from wildfire smoke comes from fine particulate matter, which can exacerbate respiratory and cardiovascular conditions and cause both short- and long-term health problems. Public health officials advise people to remain indoors and take steps to improve air quality inside their homes.

For those with central air conditioning, experts recommend ensuring that air filters are clean and replaced regularly, preferably using filters rated MERV 13 or higher. Systems should be set to recirculate air rather than draw in outside air, which may be heavily polluted. The University of Oregon’s Center for Wildfire Smoke Research and Practice advises keeping the system fan running continuously during smoke events to maximize air cleaning.

Portable air purifiers with HEPA filters or those specifically rated to trap fine pollution particles are also effective. Users should avoid devices that generate ozone, as this can present additional health risks. When resources are limited, experts suggest concentrating filtration efforts into a single “clean room” where individuals spend most of their time.

DIY options have proven effective as well. Environmental epidemiologist Amy Kalkbrenner of the University of Wisconsin-Milwaukee highlights that homemade filters—constructed by attaching MERV 13 or higher furnace filters to a box fan with duct tape—can significantly reduce indoor particulate levels. The U.S. Environmental Protection Agency has verified that these low-cost, easy-to-assemble units perform comparably to commercial air purifiers. Proper assembly involves orienting the filters so the airflow arrows point inward and ensuring airtight seals with tape.

Not all air conditioning units provide adequate filtration. Many window air conditioners, mini-splits, and portable units lack high-efficiency filters capable of capturing fine particles. Researchers caution that when smoke and heat coincide, health impacts are intensified. Jess Downey from the University of Oregon center recommends using an air purifier or a box fan filter alongside an AC unit that is well-sealed and set to recirculate indoor air. Portable air conditioners with a single exhaust hose should be used cautiously.

For individuals without air conditioning, seeking out community spaces such as libraries or shopping centers with clean, cool air can provide temporary relief. Sealing cracks and gaps around doors and windows to reduce smoke infiltration is also advised. Dr. Khalilah Gates of Northwestern Medicine suggests treating smoke intrusion like cold air drafts, using towels or tape to block entry points.

In addition, experts recommend avoiding indoor activities that produce smoke or combustion byproducts, such as burning candles, wood fireplaces, or using gas stoves, as these can further degrade indoor air quality. Preparing meals in advance to minimize cooking during smoke episodes is encouraged.

Overall, the consensus among specialists is that while no method completely eliminates wildfire smoke exposure indoors, a combination of filtration, sealing, and ventilation strategies can substantially reduce health risks during prolonged smoke events.