When the blue flame fires up on a gas stove, there's more than heat coming off the burner. Researchers at Stanford University found that among the pollutants emitted from stoves is benzene, which is linked to cancer.

Levels of benzene can reach higher than those found in secondhand tobacco smoke and the benzene pollution can spread throughout a home, according to the research.

The findings add to a growing body of scientific evidence showing that emissions within the home are more harmful than gas stove owners have been led to believe. And it comes as stoves have been dragged into the country's ongoing culture wars.

What researchers found

Stanford scientists measured benzene from gas stoves in 87 California and Colorado homes in 2022 for the paper published in the journal Environmental Science and Technology. They found both natural gas and propane stoves "emitted detectable and repeatable levels of benzene that in some homes raised indoor benzene concentrations above well-established health benchmarks."

The risks of benzene have long been known. The Centers for Disease Control and Prevention says the chemical is linked to leukemia and other blood cell cancers.

"Benzene forms in flames and other high-temperature environments, such as the flares found in oil fields and refineries. We now know that benzene also forms in the flames of gas stoves in our homes," said Rob Jackson in a statement. He's the study's senior author and a Stanford professor of earth sciences.

With one burner on high or the oven at 350 degrees, the researchers found benzene levels in a house can be worse than average levels for second-hand tobacco smoke. And they found the toxin doesn't just stay in the kitchen, it can migrate to other places, such as bedrooms.

"Good ventilation helps reduce pollutant concentrations, but we found that exhaust fans were often ineffective at eliminating benzene exposure," Jackson said. He says this is the first paper to analyze benzene emissions when a stove or oven is in use.

Researchers also tested whether cooking food - pan-frying salmon or bacon - emits benzene but found all the pollution came from the gas and not the food. That's important because the gas industry often deflects concern about pollution from its fuel, to breathing problems that can be triggered by cooking fumes.

There are no studies out there that say cooking with gas will make someone sick. This is all about increasing risks for certain illnesses.

The gas industry responds

The American Gas Association, which represents natural gas utilities, routinely casts doubt over scientific research showing that burning natural gas in homes can be unhealthy. Last year the powerful trade group criticized a peer-reviewed study showing gas stoves leak benzene even when they are turned off. The AGA offered similar criticism of a 2022 analysis, which showed 12.7% of childhood asthma cases in the U.S. can be attributed to gas stove use in homes.

The AGA said in an email that its still evaluating the study. The National Propane Gas Association, in a statement to NPR, tried to cast doubt on the peer-reviewed research. The NPGA said the Stanford paper "fails to analyze real-world environments," and suggests when cooking with gas "air quality can be managed through numerous measures, including ventilation options such as range hoods or exhaust fans."

Medical experts are starting to take stands against cooking with gas. Nitrogen dioxide emissions have been the biggest concern, because they can trigger respiratory diseases, like asthma. The American Public Health Association has labeled gas cooking stoves "a public health concern," and the American Medical Association warns that cooking with gas increases the risk of childhood asthma.

Gas stoves also emerged as a culture war issue earlier this year after Commissioner Richard Trumka, Jr., of the Consumer Product Safety Commission (CPSC), suggested that the government might consider stricter regulation of new gas stoves.

Lawmakers in the Republican-controlled U.S. House of Representatives recently introduced and passed two pieces of legislation aimed at limiting new regulations on gas stoves. One, called the "Save Our Gas Stoves Act" would block the Department of Energy from implementing proposed energy efficiency standards for ranges. Another called the "Gas Stove Protection and Freedom Act" would prohibit the CPSC from banning or further regulating the sale of gas stoves. It's unlikely either of the bills will become law with Democrats controlling the U.S. Senate and White House.

What can you do about gas stove pollution?

Gas utilities have long researched how gas stoves pollute indoor air and even developed new styles of burners that use less gas and emit less nitrogen dioxide. But manufacturers don't use them, saying they are more expensive, harder to clean and consumers aren't demanding them.

But if you're worried about pollution from cooking with a gas stove, there are some things you can do. The most obvious is to stop cooking with gas and switch to electric.

There are campaigns underway to encourage people to do that, both for health and climate reasons. The main ingredient in natural gas is methane, which leaks into the atmosphere all along the gas supply chain and is a potent greenhouse gas.

Replacing a stove is expensive, though, and there are cheaper interim solutions. You can buy a portable induction cooktop, Consumer Reports has advice here. There are other plug-in appliances, such as toaster ovens, that can reduce the amount of time necessary to use a gas stove.

And when the time comes to replace your stove, there are now government subsidies available through the climate-focused Inflation Reduction Act passed last year. The nonprofit group Rewiring America has a guide here.