The vapor from electronic cigarettes contains two previously unidentified chemicals that can cause cancer, according to a new study. The new research, published in Environmental Science & Technology, also shows that levels of harmful chemicals vary between e-cigs.

Researchers in the Lawrence Berkeley National Laboratory used two different electronic cigarettes and simulated vaping at different battery power settings. Then they analyzed the e-cigs’ vapor. They found that the vaporizers released 31 harmful chemicals, including two possibly cancer-causing compounds that had never been previously found in e-cig vapor. The amount of chemicals produced varied, based on the temperature at which liquids are "vaporized" by the device’s "heating coil." The higher the temperature inside the coil, the higher the amount of chemicals emitted. E-cigs with one heating coil instead of two also released higher chemical levels, probably because two coils better distribute the heat between them, which means their temperatures don’t climb quite as high.

E-cigs released 31 harmful chemicals

Previous studies had already shown that e-cigarettes contain toxic chemicals. In 2009, the FDA warned that some e-cigs contain diethylene glycol, an ingredient used in antifreeze. And in 2015, a study showed that aerosols from e-cigs contain formaldehyde, another carcinogen. Some of these chemicals are also found in cigarette smoke.

An e-cig with only one heating coil operated at 3.8 volts was found to emit 0.46 micrograms of acrolein — a severe eye and respiratory irritant — per puff in the first five puffs, while the coil was heating up. But when the heat got steady, the e-cig emitted much more: 8.7 micrograms per puff. The amount of acrolein released is still much less than a regular cigarette, which delivers 400 to 650 micrograms. About 20 puffs on an e-cigarette release 90 to 100 micrograms in comparison.

"Advocates of e-cigarettes say emissions are much lower than from conventional cigarettes, so you’re better off using e-cigarettes," Berkeley Lab researcher and study co-author Hugo Destaillats 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."

"Regular cigarettes are super unhealthy. E-cigarettes are just unhealthy."

Chemical emissions also changed based on the e-cig’s battery voltage. The higher the voltage, the higher the temperature in the coil — and the heat meant higher chemical amounts were released. Emissions also varied based on how long the e-cig had been used. The longer it was used, the higher the level of chemicals it released, including formaldehyde, acetaldehyde, and acrolein — which are all carcinogens or respiratory irritants. That’s because chemical residue was accumulated on or near the heating coil. As this residue was heated up, it released even more chemicals.

The researchers also analyzed two chemicals often used as solvents in e-cigs: propylene glycol and glycerin. Both are used to make artificial smoke, though little is known about whether it’s safe to heat and inhale them. The researchers found that the solvents created 31 harmful chemicals, including propylene oxide and glycidol, both of which are probable carcinogens. These two chemicals has never been reported in e-cigs before. This is possibly because e-cigarettes are relatively new compared to traditional cigarettes, which have been studied for more than 50 years.

The use of e-cigarettes has spiked

The use of e-cigarettes has spiked: the percentage of US adults who smoke e-cigs rose to 8.5 percent in 2013 from 3.3 percent in 2010. And in 2014, nearly 13 percent of adults said they tried electronic cigarettes, according to the CDC. Though some experts think e-cigs are a good alternative for regular cigarette smokers, health officials are particularly concerned about how popular vapes are among teenagers. Many e-cigs contain nicotine and could expose children to the addictive chemical. In 2015, three million American teens used e-cigs. (In May, the FDA finally banned e-cig sales to minors.) But much more research is needed to actually understand how harmful they are.

The paper’s goal was to learn more about the risks of e-cigarettes, so that manufacturers, users, and regulators can try to minimize the harm the electronic cigarettes pose. "Understanding how these compounds are formed is very important," Destaillats said. "One reason is for regulatory purposes, and the second is, if you want to manufacture a less harmful e-cigarette, you have to understand what the main sources of these carcinogens are."