Scientists are increasingly finding that wildfire smoke does more than irritate the lungs — it affects the whole body. “Your whole body is affected,” says Yang Liu, Professor of Environmental Health at Emory University. “Wildfire smoke causes oxidative stress to your system and exacerbates or accelerates the development of diseases.”
Recent studies reinforce that warning. A January 2026 study linked repeated exposure to even moderate wildfire smoke with higher stroke risk in older adults. Another paper the following month estimated that long-term exposure to wildfire smoke contributed to roughly 24,100 U.S. deaths per year between 2006 and 2020.
What makes smoke dangerous is its complex mix of pollutants, especially fine particulate matter called PM2.5. These tiny particles — made of soot, dust and other materials — can carry toxic metals and organic chemicals. When inhaled, PM2.5 can reach deep into the lungs and pass into the bloodstream, triggering inflammation and damaging organs throughout the body.
Long-term exposure to PM2.5 has been associated with a wide range of conditions, including asthma and other respiratory diseases, heart disease, diabetes, dementia and some cancers. Pregnant people are particularly at risk: exposure to wildfire smoke has been linked to greater chances of premature birth and low birth weight.
Wildfire PM2.5 often differs from everyday urban pollution because of what’s being burned. Smoke composition varies by region, fuel type and even neighborhood. Mary Johnson, a principal research scientist at the Harvard T.H. Chan School of Public Health, led an international study testing toxins in smoke from recently exposed firefighters and civilians. Her team found heavy metals such as mercury and cadmium, carcinogenic compounds and PFAS — the persistent “forever chemicals” used in many products and building materials. PFAS have been connected to cancers and metabolic disorders. Johnson and colleagues say follow-up research should prioritize finding treatments and protections for vulnerable groups, including children, older adults and people with chronic illnesses.
Smoke can also become more harmful as it ages. Chemical reactions in the atmosphere can increase its cell-damaging potential over days; researchers in Greece reported that smoke toxicity can rise up to fourfold in the days after a fire. Because smoke can travel great distances, a single large blaze can affect populations far from the burn. For example, smoke from the 2023 Canadian wildfires spread across North America and reached parts of Europe and Asia; analyses have linked those fires to thousands of acute and chronic deaths across continents.
Still, experts note that other, more continuous sources of air pollution — traffic exhaust, industrial emissions and indoor burning of fuels — contribute more to overall population mortality because exposure is constant. “When we look at what really drives mortality in the population as a whole, it’s still all these other sources [of air pollution] that are really responsible for so many deaths,” says Cathryn Tonne, an environmental epidemiologist at the Barcelona Institute for Global Health.
How to protect yourself and your family
– Reduce exposure during and immediately after fires: stay indoors with windows and doors closed when smoke is heavy.
– Improve indoor air: use high-efficiency filters in HVAC systems or portable HEPA air cleaners. Close windows and seal gaps when smoke is present.
– Use respirators when appropriate: N95- or equivalent-grade masks can reduce inhaled PM2.5 when worn correctly during short-term outdoor exposure.
– Prepare medicines and supplies: ensure people with asthma, heart disease or other chronic conditions have emergency medications and inhalers on hand.
– Prepare property and community: before fire season, clear flammable materials from around homes, maintain defensible space and coordinate neighborhood monitoring and rapid response to small fires.
While research continues on treatments and targeted protections, reducing exposure remains the most effective way to limit the health harms of wildfire smoke, especially for children, older adults and those with existing health conditions.