Electronic cigarettes appear to be safer than ordinary cigarettes for one simple — and simply obvious — reason: people don't light up and smoke them.
With the e-cigarettes, there is no burning tobacco to produce myriad new chemicals, including some 60 carcinogens.
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. A second study that is being prepared for submission to the same journal points to similar findings.
The long-term effects of inhaling nicotine vapor 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 companies have made much of in their advertising.
Articles in this series examine the multibillion-dollar market for e-cigarettes and the consequences for public health.
The website for Janty, a company that manufactures popular tank systems, says the benefits of e-cigarettes include having "no toxins associated with tobacco smoking."
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 F.D.A. has focused largely on what goes into these products — currently, an unregulated brew of chemicals and flavorings — rather than on what comes out of them, as wispy plumes of flavored vapor.
The proposed rules give the F.D.A. the power to regulate ingredients, not emissions, although the agency said it could consider such regulations in the future. Even so, some experts contend that the current approach is akin to examining the health risks associated with tobacco leaves rather than with cigarette smoke.
"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 vapor."
Both studies focused on tank systems, fast-growing members of the e-cigarette family. Unlike disposable e-cigarettes, which tend to mimic the look and feel of conventional smokes, tank systems tend to be larger devices heated with batteries that can vary in voltage, often resembling fountain pens or small flashlights. Users fill them with liquid nicotine, or e-liquid, and the devices are powerful enough to vaporize that fluid quickly, producing thick plumes and a big nicotine kick.