A new study published in Environmental Science & Technology finds that gas stoves frequently leak dangerous pollutants into the kitchen. A team from PSE Health Energy collected samples from 159 gas stoves across California and sent them to a laboratory for analysis. The researchers found 12 pollutants in total, and four of these gases—benzene, toluene, hexane and m- or p-xylene—were present in 98 percent of the samples. Most of the stoves leaked at least a little, even when they were turned off. 

The natural gas used in stoves is comprised mostly of methane and other hydrocarbons and gases. Before it is delivered into homes and business, most of the non-methane gases are removed and a strong-scented chemical is added to alert people to possible leaks. The leaks studied by the California researchers were not substantial enough for people to notice this rotten-egg smell, but they could still expose users to harmful and potentially cancer-causing pollutants. Those with gas stoves are encouraged to turn on their exhaust fans whenever they are in use.