July 30 (UPI) -- E-cigarette users are consuming unknown ingredients that are irritating their air passageways, new findings show.

When people vape, a chemical reaction forms as a vanilla flavoring chemical commonly used in e-cigarettes mixes with nicotine and flavors, according to research published Tuesday in the American Journal of Preventive Medicine. Those flavorings are known as glycerols, which react to form acetals.


While the chemical vanillin is used for vanilla flavoring in many e-cigarette flavorings, it is banned in tobacco cigarettes. While the chemical itself is subject to regulation, researchers say the way it mixes with other chemicals is just as big a concern.

"People often assume that these e-liquids are a final product once they are mixed," Hanno Erythropel, a researcher at Yale University and study lead author, said in a news release. "But the reactions create new molecules in the e-liquids, and it doesn't just happen in e-liquids from small vape shops, but also in those from the biggest manufacturers in the U.S."

The researchers created a "vaping machine" to test "Cool Cucumber," "Crème Brulée" and "Fruit Medley," and five other flavors of Juul refill cartridges. They found four of those flavors included menthol, which can increase nicotine cravings.

Juul spokesperson Ted Kwong, however, dismissed the findings as unrealistic because a user "would have to consume at least seven Juul pods, and likely much more, in a single day" to reach the exposure levels seen in the study.

"The researchers created a risk assessment model based on an occupational environmental standard for ambient air, which, as applied to analyses of vapor products, assumes a person would inhale only aerosolized vapor for eight hours per day, five days per week, for decades," Kwong told UPI. "The result was to create a false equivalence and a measurement of exposure that would never be found in the real world."

Concerns about both nicotine content and flavored vapor pods, as well as the chemicals involved, have been raised by the results of other studies as well.

Nicotine content in e-cigarettes flavorings are equal to two packs of tobacco cigarettes, leading to an addiction epidemic young people, one study suggests. And previous research has shown that e-cigarette flavorings have led to an increase in flavored tobacco use among teens.

The researchers hope in the future that e-cigarette packaging will disclose the fact that vaping may create potentially serious compounds that could lead to unknown health effects.

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"We were surprised that levels in Juul vapor were already close to safety limits for workplaces where vanillin is used, such as in bakeries and the flavor chemical industry," said Sven-Eric Jordt, a researcher at Duke University and study co-author.