In the paper, researchers detected significant levels of 31 toxic chemicals, including formaldehyde, acrolein, propylene oxide, and previously undetected glycidol present. Acrolein is used as a herbicide and is found in conventional cigarettes. Glycidol is an irritant that's a potential carcinogen, as is propylene oxide. Formaldehyde, of course, is the tobacco industry's most famous carcinogen. These and other toxins increased several-fold after sustained use of the vape, after it heated up around 20 puffs. High temperatures meant more harmful emissions.