Electronic cigarettes appear to be safer than ordinary cigarettes for one obvious reason: People don't light up and smoke them.
But new research suggests that, even without a match, some popular e-cigarettes get so hot that they, too, can produce a handful of the carcinogens found in cigarettes and at similar levels.
A study to be published this month in the journal Nicotine and Tobacco Research found that the high-power e-cigarettes known as tank systems produce formaldehyde, a known carcinogen, along with the nicotine-laced vapor that their users inhale. The toxin is formed when liquid nicotine and other e-cigarette ingredients are subjected to high temperatures, according to the study.
The long-term effects of inhaling nicotine vapour are unclear, but there is no evidence to date that it causes cancer or heart disease as cigarette smoking does. Indeed, many researchers agree that e-cigarettes will turn out to be much safer than conventional cigarettes, an idea that e-cigarette firms have made much of in their advertising.
Nonetheless, the new research suggests how potential health risks are emerging as the multibillion-dollar e-cigarette business rapidly evolves, and how regulators are already struggling to keep pace. While the Food and Drug Administration last month proposed sweeping new rules that for the first time would extend its authority to e-cigarettes, the FDA has focused largely on what goes into these products - currently, an unregulated brew of chemicals and flavourings - rather than on what comes out of them, as wispy plumes of flavoured vapor.
The proposed rules give the FDA the power to regulate ingredients, not emissions, although the agency said it could consider such regulations going forward.
"Looking at ingredients is one thing, and very important," said Maciej L. Goniewicz, who led the first study, which is scheduled to be published on May 15. "But to have a comprehensive picture, you have to look at the vapour."
Both studies focused on tank systems, fast-growing members of the e-cigarette family. Unlike disposable e-cigarettes, tank systems tend to be larger and with batteries of varying voltage. Users fill them with liquid nicotine, and the devices are powerful enough to vaporise that fluid quickly.
Goniewicz, an assistant professor of oncology at the Roswell Park Cancer Institute in Buffalo, New York, said people using the systems "want more nicotine, but the problem is they're also getting more toxicants [sic]."