Tina Johnson’s kitchen hasn’t changed much over the years. Her gas stove anchors the room, its click and blue flames a signal to her family that it’s time for a meal.

But testing done in her home in the Harlem neighborhood of New York and in others across the country show that people with gas and propane stoves breathe in unhealthy levels of nitrogen dioxide, which can trigger asthma and other respiratory conditions, according to a new study Stanford University researchers published Friday in the journal Science Advances.

The new research estimates that long-term exposure to the staple kitchen appliance could be responsible for 50,000 current pediatric asthma cases from nitrogen dioxide.

The study found that the nitrogen dioxide emitted from stoves didn’t just linger in the kitchen area but impacted the entire home – in some cases hours after the stove was turned off. Indigenous, Alaska Native, Hispanic and Black households, as well as low-income households, experience the highest exposure to nitrogen dioxide from gas and propane from cooking, the study found.

The study adds to the growing body of evidence that shows cooking with a gas stove creates indoor air pollution that can be harmful to human health. Friday’s study directly estimates health outcomes of nitrogen dioxide due to gas and propane stoves, and how those exposure levels vary based on housing sizing, ventilation practices and race and ethnicity.

“It compounds the injustice of air pollution: Poorer people, and often minority communities, breathe dirtier air outdoors all the time. And it turns out they also breathe dirtier air indoors. And it’s not fair,” said Rob Jackson, the principal investigator for this research.

People living in smaller residences, 800 square feet or less, were exposed to the highest concentrations of nitrogen dioxide, according to the study – more than four times the amount of long-term nitrogen dioxide concentrations for people in larger homes.

“Everyone in the home is paying the price or the cost for that, for breathing this pollution,” said Jackson, a professor of earth system science at Stanford’s Doerr School of Sustainability.

In half of the tested homes, bedroom nitrogen dioxide concentrations exceeded the Environmental Protection Agency’s and the World Health Organization’s hourly guidelines within 25 minutes of oven use.

Scientists measured nitrogen dioxide concentrations from more than 100 homes and used other data sets – like home size, ventilation practices, cooking habits – to create an indoor air quality model and exposure estimates. They then used those exposure estimates to determine health risk estimates for asthma and mortality.

Based on the model, researchers estimate that long-term exposure to nitrogen dioxide from gas and propane stoves could be responsible for up to 19,000 adult deaths annually across the country – although combinations of nitrogen dioxide and other outdoor pollution could impact the estimate.

The American Gas Association, a trade group, said previous research that the Stanford scientists used to help determine the number of pediatric asthma cases and adult deaths shows no association between cooking with gas and childhood asthma and cautioned against concluding that outdoor exposure to nitrogen dioxide could include the risk of dying. The analysis of the previous research does not support the results of Friday’s study, the association said.

“Despite the impressive names on this study, the data presented here clearly does not support any linkages between gas stoves and childhood asthma or adult mortality,” said American Gas Association President and CEO Karen Harbert. “The two major cited studies used to underpin the Stanford analysis directly contradict the conclusions they have presented. In short, the interpretation of results … are misleading and unsupported.”

Researchers said numerous other studies, including the ones they cited, have shown the link between asthma and gas stoves.

Yannai Kashtan, the lead author of the study and a PhD candidate in the earth system science program at Stanford, said that by having and using a gas stove, people are exposed to three-quarters of the annual nitrogen dioxide guidelines set forth by the World Health Organization, absent “all the other outdoor sources of nitrogen dioxide … in our lives from traffic, power plants and other combustion sources.” The EPA has limits for outside nitrogen dioxide exposure but does not regulate indoor air pollution.

Gas stoves also release formaldehyde and benzene, a known carcinogen, and the study’s researchers said the overall exposure to pollutants from gas stoves could be responsible for 200,000 cases of childhood asthma each year.

Michael Johnson, the technical director at Berkeley Air Monitoring Group, said that randomized controlled trials are needed instead of the modeling that the Stanford researchers used in the study to better understand the health impacts from gas stoves.

“It’s not that I don’t think there are health impacts from using gas stoves. There almost certainly are. But, trying to estimate what those health impacts are would need some type of randomized controlled trial,” Michael Johnson said. Modeling allows uncertainty to seep into estimates of health impacts, he said. Despite this, Michael Johnson said the study is the strongest he has seen at modeling how gas stoves impact health.

“From a public health perspective, we just shouldn’t be using technologies that expose us to excess health risk by doing something as fundamental as cooking. In that sense, I don’t think the precision of the numbers is that important,” Michael Johnson said.

In Tina Johnson’s apartment, with the kitchen windows closed and one burner on, nitrogen dioxide levels reached five times the hourly benchmarks from the EPA and WHO. With the window open and the air circulating to the rest of the home, nitrogen dioxide levels doubled from the EPA and WHO hourly benchmarks.

Tina Johnson said she had always been a bit worried about the fumes that came from her gas stove, and the measurements she read from researchers reignited her fears.

“I feel beat down by the whole process and the results,” said Johnson, 57.

The study showed that reducing indoor air pollution from gas and propane stoves yields varying results based on the effectiveness of different ventilation hoods. Some outside-venting range hoods push pollution concentrations outside through pipes, while others work like recirculating fans: reducing pollution levels around the stove but spreading them around the home. Across five randomly selected homes, different hoods reduced hourly kitchen nitrogen dioxide concentrations between 10 to 70 percent.

Kashtan hopes that more attention on the issue will encourage politicians to regulate indoor air quality and urge people to move toward safer appliances.

“As a country we are doing a good job cleaning up our outdoor air by reducing fossil fuel use, but our indoor air is lagging behind. I hope this study drives home the importance of indoor air quality, to the public and to regulators,” he said.

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