Electronic cigarettes may produce an aerosol vapor instead of smoke, but two new studies raise burning questions about their uses and risks.

E-cigs—as these battery-operated nicotine inhalers are commonly called—are increasingly popular, with a Wells Fargo financial analyst predicting that U.S. sales will double this year, going up to $1.7 billion.

Their visibility is becoming ever greater as well, with television and online marketing campaigns that feature celebrities like Jenny McCarthy and Stephen Dorff touting the pleasures of what they describe as more socially acceptable, "guilt-free" smoking.

The reasoning behind such claims is that e-cigs, which have the look of conventional cigarettes stylishly updated for the techno-age, produce vapor instead of ash or smoke. They also generally deliver lower amounts of nicotine than conventional cigarettes—a feature that may make e-cigarettes useful as an aid to smoking cessation.

Research Urgently Needed

Whether that is so was the focus of a study published in The Lancet, which concluded that e-cigarettes were statistically comparable to nicotine patches in helping smokers quit over a six-month period.

But this was only the first study to compare e-cigarettes to an already established quitting aid. "There is still so much that is unknown about the effectiveness and long-term effects of e-cigarettes" that more research is "urgently needed," cautioned lead researcher Chris Bullen, director of the National Institute for Health Innovation at the University of Auckland in New Zealand.

In that vein, Alexander Prokhorov, a smoking cessation expert at Houston's MD Anderson Cancer Center who was not involved in the study, commented, "I'm glad that there is finally some tangible research starting to appear." But several aspects worry him. "Nicotine is not a neutral substance," and in addition to being highly addictive, "it can be a poisonous substance."

Because e-cigs mimic the look and rituals of conventional cigarette smoking, there is a danger that rather than e-cigs helping you quit, "you may just switch to this product and continue using it," Prokhorov said. And since a smoker's dependence on nicotine remains, there is a risk for a relapse to smoking conventional cigarettes.

Not a Risk-Free Alternative

Still, wouldn't there be some potential benefit to using only electronic cigarettes as an alternative to conventional cigarettes? "There is no question that e-cigarettes deliver less toxins than conventional cigarettes," said Stanton Glantz, director of the University of California, San Francisco's Center for Tobacco Control Research and Education. They may have as little as one-tenth of the toxins inhaled from burning tobacco, he said. (Related: "Cigarettes vs. e-Cigarettes: Which Is Less Environmentally Harmful?")

But that's not the entire story, he emphasized. "Whereas e-cigarettes are less dangerous than regular cigarettes, in an absolute sense they are negative," because they contain a number of toxic chemicals and ultrafine particles in addition to nicotine, and secondhand e-cig vapor could be harmful.

Moreover, he continued, "most people who use e-cigarettes also continue to use regular cigarettes; they are dual users. That means they are probably suffering all the risks from smoking."

There is also a quality control issue for e-cigarettes, both Glantz and Prokhorov agreed. Unlike prescription nicotine patches, no electronic cigarettes have been approved for therapeutic use by the U.S. Food and Drug Administration.

"Further research is needed to assess the potential public health benefits and risks of electronic cigarettes and other novel tobacco products," said FDA spokesperson Jennifer Haliski. (Although the FDA's authority extends only to those e-cigs marketed for therapeutic purpose, with none having gained approval, it has announced its intention to propose broadening regulations to encompass additional categories of tobacco products that would include all electronic cigarettes.)

That's an important point, said Glantz, because the Lancet study's bottom line is that electronic cigarettes "are no worse than nicotine patches, but they are no better either." That leads to the question: "Why would you use something that has not been tested when there is something [with] quality control and [that] has been tested?"

Gateway Cigs for Teens?

Another question, about the average age of electronic cigarette users, brings us to the second study. This one, conducted by the Centers for Disease Control and Prevention, shows that the number of U.S. middle and high school students using e-cigarettes doubled between 2011 and 2012, bringing the number nationwide who had tried e-cigs to 1.78 million.

That statistic is disturbing, said Tim McAfee, director of the CDC's Office on Smoking and Health, because about 90 percent of all smokers begin in their teens. E-cigarettes may be particularly attractive to youngsters because they are sold in a broad array of flavors, including cherry, vanilla, and even bubblegum.

"We know that this makes these products more appealing to children," he said. "The worry is that it is going to acclimatize kids to the behaviors that are like smoking. Until proven otherwise, we need to assume that this may increase their chances of taking up smoking with burn [conventional] cigarettes." Prokhorov shares that worry.

"My major concern is that this will be a gateway behavior, a potential risk of getting kids hooked on nicotine for life," he said. That's also why Glantz favors greater regulations, including banning the use of flavors (which are prohibited in conventional tobacco cigarettes) as well as prohibiting the sale of e-cigs to minors.

"In the current world, where cigarettes are ubiquitous with a marketing budget of $8 billion a year, we have to be careful and not make it easy" for vulnerable children to start using tobacco, said McAfee, whose budget for the CDC's 2012 Tips from Former Smokers campaign was $54 million.

"You go on YouTube and see how e-cigarettes are being glamorized, making smoking look sexy and rebellious," he said, which are the very elements that research has shown will attract kids to smoking. This is why media critics are comparing current e-cig ads to the ubiquitous cigarette ads of the 1950s, he added.