Clarification: An earlier version of this story included an outdated number for states that have put in place age restrictions on sales of e-cigarettes. That figure stands at 38. In addition, the story should have made clear that Minnesota is the only state to tax e-cigarette at a rate comparable to traditional cigarettes. North Carolina also recently began taxing e-cigarettes, though at a much lower rate.

A clerk displays a blutane lighter, left, and a blu e-cigarette at a shop in Brookline, Mass. (Steven Senne/AP)

The electronic cigarette market is booming both online and in brick-and-mortar retail outlets in ways hardly imaginable half a decade ago, and the growth continues to be largely unregulated, according to a series of studies published Monday in the journal Tobacco Control.

“It’s exploding,” said Shu-Hong Zhu, a professor in the Department of Family and Preventive Medicine at the University of California at San Diego, who co-authored one of nine studies funded by the National Cancer Institute. “There’s no sign of slowing down.”

Zhu and other researchers found a “staggering” proliferation of e-cigarette brands and flavors on the Internet in the past two years alone, with roughly 10 new brands and 240 new flavors arriving on the market every month. As of January, researchers trawling English-language Web sites identified 466 e-cigarette brands and 7,764 flavors, from peppermint to piña colada.

But e-cigarettes have gained traction far beyond the Internet. Other researchers found that nearly a third of U.S. convenience stores, pharmacies and other retailers near schools sell e-cigarettes — a statistic that raises concern among some anti-smoking advocates who say there are too few barriers to youth access to the products.

“There’s this really rapid growth happening,” said Frank Chaloupka, director of the Health Policy Center at the University of Illinois at Chicago and author of several of Monday’s studies. “They are becoming available all over the place, they are being marketed aggressively, and they are cheap compared to normal cigarettes. But in terms of policy, there’s been very little done to control [the market] to this point.”

E-cigarettes and the law

The increasing popularity of e-cigarettes — devices that generally resemble traditional cigarettes but, instead of burning tobacco, heat nicotine-laced liquid into a vapor that the user inhales — has been well documented in recent years.

But as the ever-changing and vast $2 billion market continues to expand, researchers involved in Monday’s studies said the feverish growth underscores the need for more oversight and more research into the potential impact on public health.

At the least, Zhu and Chaloupka said, lawmakers should act quickly to pass measures to limit sales and marketing of e-cigarettes to minors and to ensure sound manufacturing practices.

“That’s the most important regulation that needs to be done, and it should be done quickly,” Zhu said.

Dozens of states have put in place some regulations for e-cigarettes, but so far the rules are neither uniform nor comprehensive. More than three dozen states currently prohibit the sale of e-cigarettes to minors, and that number is likely to climb. About a dozen states have enacted some form of usage ban in public places such as schools and government buildings, though only three — New Jersey, North Dakota and Utah — forbid the use of e-cigarettes everywhere that smoking is banned. Numerous municipalities also have instituted usage restrictions.

Meanwhile, Minnesota remains the only state that taxes e-cigarettes at the high rate that also applies to traditional tobacco products. North Carolina recently put in place a much more modest tax of 5 cents for each milliliter of the nicotine liquid.

In April, after years of speculation, the Food and Drug Administration said it would for the first time begin regulating e-cigarettes, as well as cigars, pipe tobacco and hookahs.

If adopted, the government’s plan would force manufacturers to curb sales to minors, stop handing out free samples, place health warning labels on their products and disclose the ingredients. Makers of e-cigarettes would be banned from making health-related claims without scientific evidence.

But the FDA’s proposal would not seek to restrict online sales of e-cigarettes, curb television advertising or ban the widespread use of exotic flavors, which tobacco-control advocates have argued helps to attract young smokers and which have been banned for traditional cigarettes. Given the sluggish nature of the federal rule-writing process and the prospect of litigation over the proposed rules, any final regulations are probably years away.

“The industry has no problem with regulation. The industry has a problem with inappropriate regulation,” said Cynthia Cabrera, executive director of the Smoke-Free Alternatives Trade Association, who had not yet seen the details of Monday’s studies. “If you have regulation that stifles this market, that’s not a good thing.”

Cabrera said her group supports a national age restriction on e-cigarettes and the majority of companies have been diligent in putting strict age-verification checks in place, both online and in retail outlets. She added that reputable e-cigarette makers adhere to stringent manufacturing practices.

Cabrera also said that many e-cigarette users are cigarette smokers who are trying to kick tobacco habits.

“If current smokers are switching over to vaporizing products, then great,” she said.

Zhu, the UC-San Diego researcher, agreed that e-cigarettes could end up providing a net benefit if they lessen use of tobacco. But he said that what’s missing is basic regulation of the industry and more reliable research into e-cigarettes’ long-term impact on health. “We want to regulate e-cigarettes in such a way that we help reduce cigarette smoking as much as possible,” he said.

Another study released Monday offered an additional glimpse at who seems to be attracted to e-cigarettes, at least in Europe. Researchers there analyzed nearly 27,000 e-cigarette users from 27 countries in the European Union.

The results showed that users were more likely to be young, between 15 and 24. They also were more likely to be cigarette smokers who have made at least one attempt to quit in the past year.