By Gabe Castro-Root

Gas stoves, which are used in a majority of California households, can emit a chemical linked to cancer at levels higher than those caused by secondhand tobacco smoke, a new study from Stanford researchers found.

The chemical benzene can spread far from the kitchen and linger inside for hours at levels that have prompted investigations when detected outdoors, according to the peer-reviewed study published last week in the journal Environmental Science & Technology.

“We would never willingly stand over the tailpipe of a car, breathing in its pollution,” said Rob Jackson, an environmental scientist at Stanford and the study’s principal investigator. But that’s essentially what happens when cooking over a gas flame, he said at a media briefing Tuesday.

“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 Jackson. “Good ventilation helps reduce pollutant concentrations, but we found that exhaust fans were often ineffective at eliminating benzene exposure.”

A single gas burner on high or a gas oven at 350 degrees can raise indoor benzene levels above national and international health benchmarks, according to the study.

The findings have especially large implications for California, where 70% of households use natural gas for cooking, as of the latest data in 2020, compared with about 38% nationally, according to the U.S. Energy Information Administration.

“Benzene is a carcinogen — there is no safe level of exposure,” according to a short video by the Stanford Woods Institute for the Environment explaining the findings. The video shows animated benzene particles spreading from the kitchen to four other rooms on three floors of a house.

The researchers noted that benzene at chronic low-dose exposure has been linked to a variety of blood cancers, including non-Hodgkin’s lymphoma and multiple types of leukemia. Their study was the first to measure indoor benzene levels emitted from a stove’s flame, the researchers said.

They measured benzene from stoves in 87 homes in Colorado and California, including the greater Bay Area counties of Santa Clara, San Mateo, Alameda, Contra Costa, Santa Cruz and Mendocino and the counties of Kern, Los Angeles, Orange and Riverside.

In some cases, it took six hours or more for the concentration of benzene in bedrooms to return to baseline levels after using a gas stove several rooms away.

By comparison, benzene emissions from electric and induction stovetops — as well as from the process of the food itself being cooked — are minuscule or zero in some cases, the researchers found.

The researchers also recently visited apartments in New York City to see how far pollutants from gas stoves traveled in a higher-density environment.

“It is pretty straightforward to say that if you have a smaller space, you will be diluting emissions less and so their concentration will be higher,” said Yannai Kashtan, a graduate student at Stanford’s Doerr School and the study’s lead author.

Gas stoves have become a political flash point as federal regulators consider moves to tighten indoor air quality standards and some local governments seek to phase out gas appliances completely.

The Bay Area Air Quality Management District voted earlier this year to phase out natural gas furnaces and water heaters, but left gas stoves untouched because its authority does not extend to the air within homes. Still, the move prompted unfounded fears of gas stoves being removed.

A federal appeals court in April struck down Berkeley’s ban on natural gas lines in new construction, the first such regulation in the nation.

Just last week, the Republican-controlled U.S. House of Representatives passed bills to prohibit the Energy Department from boosting efficiency standards for stoves and ovens and to prevent the use of federal money to regulate gas stoves. Neither measure was expected to pass the Democratic-majority Senate.

The American Gas Association, a trade group that applauded the recent House-passed bills, did not immediately respond to a request for comment about the Stanford study.

The Stanford researchers recommend switching to induction stoves as the best method of protection against benzene emissions. Those can be comparatively expensive, but some portable electric burners sell for as little as $50.

A variety of federal, state and local rebates are also available to help reduce the cost of switching to electric appliances.

“This study does point out that people have died from exposure in homes, and unless this problem is ameliorated, will continue to,” said Dr. Jan Kirsch, a blood cancer specialist, at the media briefing.

But the research isn’t a reason to panic, she said. “There are risks, and we want to reduce them.”