UPI reports e-cigarette users are inhaling unknown ingredients that are irritating their air passageways.
When people vape, a chemical reaction forms in which vanilla-flavored glycerols turn to acetals.
Researchers created a "vaping machine" to test eight different flavors of Juul refill cartridges.
They found four of those flavors included menthol, which can increase nicotine cravings.
The nicotine content of e-cigarette flavorings are equal to two packs of tobacco cigarettes.
