When wildfires rage, we often fear the flames, but the danger can last much longer. A recent study by Dr. Hugo Destaillats and Dr. Wanyu R. Chan in the journal Indoor Environments examines how wildfire smoke can enter indoors and leave behind harmful residue that sticks to surfaces and lingers in the air.

Even after the visible smoke clears, tiny particles and chemicals from wildfires settle in homes, cars, and on furniture. These can be released back into the air, where people breathe them in or even absorb them through their skin. This residue includes fine particles, gases, and volatile organic compounds. They are all invisible yet harmful.

This is similar to what scientists call thirdhand smoke from cigarettes or thirdhand chemical residue from vaping. After smoking stops, toxic tobacco chemicals like nicotine and other harmful substances remain on walls, clothes, carpets, and toys. Children, in particular, are at risk because they crawl, touch, and sometimes put contaminated objects in their mouths.

Wildfire residue and thirdhand tobacco smoke share a hidden danger — even when active smoke disappears, the toxic leftovers can continue to put health at risk. Negative health effects may include irritation in the eyes, throat, and nose, respiratory issues, and long-term risks that aren’t always obvious right away.

Here’s what you can do to protect yourself and your family:

• Seal your space when wildfire smoke is heavy. During wildfire season or if someone is smoking nearby, close windows and doors to reduce indoor contamination.
• Use air purifiers. A HEPA-filter air purifier can capture fine particles; if possible, select one that also combines HEPA and activated carbon to address gases and odors.
• Clean smartly. Wash hard surfaces with a mild detergent, vacuum using a HEPA filter, and launder clothes and fabrics that might retain residue. Replace HVAC or air purifier filters after smoke events.
• Create smokefree zones. Never allow tobacco use indoors or outdoors near doors and windows — it’s the best way to prevent thirdhand tobacco smoke from building up.
• Keep an eye on air quality. Stay updated during wildfire season and wear masks (N95 or similar) if you need to go outside when the air is bad.

Understanding that smoke can leave a “toxic footprint” after the flames or cigarettes are gone is crucial. Whether the source is wildfire or tobacco, these residues can continue to impact our health unless we take steps to clean and protect our air. By sealing up, cleaning surfaces, using filters, and preventing indoor smoking, we can all breathe easier and keep our homes healthier.

This text was initially drafted by ChatGPT 5.0. The text was reviewed, modified, and finalized by members of the Thirdhand Smoke Resource Center.

Click here to read the research study.