But the higher temperatures also can trigger a thermal breakdown of the solvents, producing the carbonyls, explains Maciej Goniewicz of the Roswell Park Cancer Institute in Buffalo, N.Y. If users of second-generation e-cigarettes maximize the power on their devices while using vaping liquids containing a solvent mix of glycerin and propylene glycol, formaldehyde levels can reach that found in tobacco smoke, his team reports May 15 in Nicotine & Tobacco Research.
Such compounds in smoke are mainly a concern if they make it all the way into the lungs. Many biologists think particle size and count are key, says Glantz. Vapers can inhale huge numbers of very small aerosols — the most toxic size — that can then deposit into the lung’s tiniest airways, which are pivotal to moving air into the body.