Lighting a fire on a cold winter night can feel cozy. But a new study suggests it may also harm your health, even if you don’t burn the wood yourself.

Researchers at Northwestern University found that home wood burning is responsible for about 22% of outdoor fine particle pollution (PM2.5) during winter across the U.S.

That’s despite the fact that only 2% of households use wood as their main heat source.

PM2.5 particles are tiny and dangerous. They can move deep into the lungs and even enter the bloodstream.

Long-term exposure has been linked to heart disease, lung disease and premature death.

The research team estimates that pollution from residential wood burning is tied to about 8,600 premature deaths each year.

The study was published Jan. 23 in the journal Science Advances.

"Long-term exposure to fine particulate matter is associated with an increased risk of cardiovascular diseases," said lead author Kyan Shlipak, an undergraduate mechanical engineering student at Northwestern University. 

"Studies have shown consistently that this exposure leads to a higher risk of death," he added in a news release. "Our study suggests that one way to substantially reduce this pollution is to reduce residential wood burning."

Shlipak noted that "using alternative appliances to heat homes instead of burning wood would have a big impact on fine particulate matter in the air."

One surprising finding: Urban areas are hardest-hit.

Smoke from wood-burning suburban homes often drifts into nearby cities, where more people live. As a result, many city residents breathe polluted air even if they don't use fireplaces or wood stoves.

People of color are especially affected.

Although they tend to burn less wood, they face higher exposure and worse health outcomes.

In the Chicago area, Black communities experienced more than 30% higher health impacts from wood smoke compared to the citywide average.

"While a lot of emissions from residential wood burning come from the suburbs, pollutants emitted into the air don't typically stay put," said senior author Daniel Horton, an assistant professor of earth and planetary sciences at Northwestern. "When this pollution is transported over densely populated cities, more people are exposed."

He continued: "Because people of color tend to be more susceptible to environmental stressors due to the long tail of past discriminatory policies, we estimate larger negative health outcomes for people of color."

Wildfires often get attention for poor air quality. But pollution from everyday home heating usually does not.

"We frequently hear about the negative health impacts of wildfire smoke, but do not often consider the consequences of burning wood for heat in our homes," Horton said.

Using detailed U.S. Environmental Protection Agency (EPA) data and computer models, the researchers tracked how smoke travels neighborhood by neighborhood.

They found that residential wood burning is one of the largest sources of fine particle pollution during winter.

The study looked only at outdoor air. It did not include indoor smoke exposure, which can also be harmful.