• Posted July 1, 2025

Wildfire Smoke Alters Immune System, Study Says

TUESDAY, July 1, 2025 (HealthDay News) —Exposure to wildfire smoke might make some people more likely to fall ill by altering their immune systems, a new study says.

Fire smoke appears to affect the immune system on a cellular level, researchers report in the journal Nature Medicine.

People exposed to smoke showed an increase in memory immune cells that provide long-term immunity and biomarkers of increased inflammation and immune activity, results show.

They also showed changes in dozens of genes related to allergies and asthma, researchers said.

“We’ve known that smoke exposure causes poor respiratory, cardiac, neurological and pregnancy outcomes, but we haven’t understood how,” senior researcher Dr. Kari Nadeau, chair of environmental health at the Harvard TH Chan School of Public Health, said in a news release.

“Our study fills in this knowledge gap, so that clinicians and public health leaders are better equipped to respond to the growing threat of difficult-to-contain toxic wildfires,” she added.

Fire smoke is filled with all sorts of matter that can affect the body – fine particle pollution, “forever” PFAS chemicals, toxic metals and gases, and even cancer-causing compounds, researchers said in a news release.

To test smoke’s effect on the body, researchers collected blood samples from 31 firefighters and civilians and compared them to those from 29 people not exposed to smoke.

Results show that smoke-exposed people had more immune cells affected by toxic metals like mercury and cadmium.

They also had changes in 133 genes related to allergies and asthma, and increased signs of immune response and inflammation, researchers said.

“Our findings demonstrate that the immune system is extremely sensitive to environmental exposures like fire smoke, even in healthy individuals,” lead researcher Dr. Mary Johnson, a principal research scientist of environmental health at the Chan School, said in a news release.

“Knowing exactly how may help us detect immune dysfunction from smoke exposure earlier and could pave the way for new therapeutics to mitigate, or prevent altogether, the health effects of smoke exposure and environmental contaminants,” Johnson said.

Understanding smoke’s effects on the immune system also could help public health officials better prepare the public for wildfire season, researchers added.

“Knowing more about exactly how smoke exposure is harming the body, we may increase public health campaigns about the dangers of smoke exposure and the importance of following evacuation procedures during wildfires,” Nadeau said. “We may also reconsider what levels of smoke exposure we consider toxic.”

More information

The U.S. Centers for Disease Control and Prevention has more on how wildfire smoke affects the body.

SOURCE: Harvard TH Chan School of Public Health, news release, June 26, 2025