Vapor from electronic cigarettes contains two previously undiscovered cancer-causing chemicals, according to a new study.

Researchers at the Lawrence Berkeley National Laboratory found propylene glycol, an eye and respiratory irritant, and glycerin, a skin, eye and respiratory irritant, among 29 other chemicals released in e-cigarette vapor.

Both are considered “probable carcinogens” by federal health officials. They’re used in e-cigarettes to create artificial smoke.

Decomposition of those chemicals, caused by heating them inside an e-cig, also releases toxic chemicals such as acrolein and formaldehyde, according to the study published in the journal Environmental Science and Technology.

“Advocates of e-cigarettes say emissions are much lower than from conventional cigarettes, so you’re better off using e-cigarettes,” Hugo Destaillats, the study’s author and Berkeley Lab researcher, said in a statement.

“I would say, that may be true for certain users — for example, long time smokers that cannot quit — but the problem is, it doesn’t mean that they’re healthy. Regular cigarettes are super unhealthy. E-cigarettes are just unhealthy,” he said.

Researchers simulated “vaping” with three types of “e-liquids” in two vaporizers operated at different battery settings.

The higher the temperature inside the vaporizer’s heating coil, the more chemicals were emitted. E-cigs with one heating coil instead of two released higher amounts of chemicals because the coil was hotter, the study found.

And puffs taken at different times released varying amounts of chemicals, the research showed. Vapes taken while an e-cig was heating up released lower levels of chemicals than when the device was used at a “steady state” with constant heat.

Previous studies have already shown e-cigarettes emit toxic chemicals. The FDA in 2009 warned that some e-cigarettes emit diethylene glycol, a chemical used in antifreeze. A 2015 study in the New England Journal of Medicine found e-cigs give off formaldehyde, another carcinogen.

And e-cigarette use has also spiked in the United States. More than 13 percent of middle and high school students in 2014 had used an e-cigarette, triple the number that had used them the year before, according to the Centers for Disease Control and Prevention .

Almost 13 percent of adults, and more than 21 percent of adults aged 18 to 24, reported using e-cigarettes in 2014, the CDC found .

The FDA banned the sale of e-cigs to minors in May.

(c) 2016, The Washington Post · Jacob Bogage