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Electronic cigarettes appear to be safer than ordinary cigarettes for one simple 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 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 being prepared for submission to the same journal points to similar findings.

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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. 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. 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 (FDA) last month proposed 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 flavorings — rather than on what comes out of them, as wispy plumes of flavored vapor.

The proposed rules give the FDA 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 Goniewicz, who led the first study, which is scheduled to be published 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.

Goniewicz, an assistant professor of oncology at the Roswell Park Cancer Institute in Buffalo, N.Y., said people using the systems “want more nicotine, but the problem is they’re also getting more toxicants.”

Like Goniewicz’s study, which has been subjected to peer review, the second study also centered on the impact of increased heat generated by the systems.

In that study, the focus was on how people use the devices to create more — and more potent — vapor. Rather than fill their tank systems with e-liquid, experienced users often trickle drops of the fluid directly onto the device’s heating element, a practice known as “dripping.”

But with dripping, the e-liquid heats with such intensity that formaldehyde and related toxins “approach the concentration in cigarettes,” said Alan Shihadeh, a project director at the Virginia Commonwealth University’s Center for the Study of Tobacco Products and an associate professor of mechanical engineering at American University in Beirut, who led the research.

Both studies point to the same phenomenon: Intense heat can change the composition of e-liquids, creating new chemicals. Importantly, the researchers said, the chemical reactions apply not only to the liquid nicotine, but also to two other crucial ingredients in most e-liquids: vegetable glycerin and propylene glycol.

Both studies examined only a handful of carcinogens. Traditional cigarettes, by contrast, create thousands of chemicals and dozens of carcinogens, according to Prue Talbot, professor of cell biology at the University of California, Riverside.

E-cigarettes do not tend to generate enough heat to create combustion, which is a big reason that many public health officials and researchers predict they will prove less harmful than cigarettes.

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