And suspicions about these unregulated devices are not unfounded. The FDA survey of e-cigarettes found that one brand, Smoking Everywhere, contained diethylene glycol, a toxic chemical found in antifreeze.
Marketing of these e-cigarettes has also been controversial. The main selling point for some advertisements is that you can puff on e-cigarettes in places that would normally ban smoking such as the office, restaurants, even airplanes.
And this is certainly a draw for most users: one California man, who wished to remain anonymous, is able to use his in the bathroom of the hospital where he works without detection.
The potential for subjecting non-smokers to the vapor of e-cigarettes led Americans for Nonsmokers' Rights to rally for bans on using them in public places:
"We don't know if the vapor is truly safe. We just don't know that much about e-cigarettes. For every environment that's already smoke-free, we believe it should be e-cigarette free," says Cynthia Hallet, executive director.
The ease of concealing an e-cigarette habit (no smoke, no smell) may also make the product more appealing to teens, some argue, and certain brands of e-cigarettes have also been accused of marketing to kids by offering candy-like flavors such as chocolate, cherry, mocha, or almond.
Though he doesn't know any teens who have latched onto the habit, Dr. Petros Levounis, director of the Addiction Institute of New York, says that "there is definitely reason for concern here."
Because teens can get them online by pretending to satisfy the age restrictions many brands place on their websites, "I wouldn't be surprised if this becomes a problem," he says.
Even if e-cigarettes lack the toxicity of tobacco cigarettes, the nicotine in them is still a stimulant substance that you would want to keep out of the hands of minors, just as you would caffeine or alcohol, says Dr. Edwin Salsitz of the Division of Chemical Dependency at Beth Israel Medical Center.
Even with the controversy, e-cigarettes have increased in popularity since appearing in the U.S. about three years ago.
Complete with an LCD light that mimics a butt's glowing ember, e-cigarettes are designed to replicate the experience of smoking. An onlooker wouldn't even notice that it is vapor blowing from the "smoker's" lips, not smoke.
What isn't replicated, however, is the tar, laundry list of harsh chemicals, or many of the side effects associated with tobacco cigarettes.
"Nicotine alone is generally not harmful, it's the other stuff in cigarettes, the carbon monoxide [produced] and other thousands of chemicals," says Salsitz. And while tobacco cigarettes are affectionately called "cancer sticks" by some users, a preliminary survey by the FDA found that e-cigarettes have only trace levels of carcinogens.
As a result, many users report that their lungs function and sense of smell and taste return after a few weeks of using e-cigarettes -- benefits often noted by those who quit smoking altogether.
"I feel like a non-smoker," says Shannon Wright, 34, of Charlotte, N.C., who smoked a pack a day for 14 years prior to finding e-cigarettes in a mall kiosk. "My morning cough that haunted me every day is gone. I have two kids and I wanted to stop smoking. This has been the only thing that has worked."