TORONTO -- You may not have known what an e-cigarette was at the start of 2013. But chances are, you do now.

Leo DiCaprio and Katherine Heigl puff on them. Talk show host Jenny McCarthy and actor Stephen Dorff hawk them. For that matter, so does Santa Claus (at least in one controversial billboard).

A telltale sign of the burgeoning popularity of e-cigarettes: Internet searches for the products have grown exponentially in recent years. A study by U.S. researchers showed a several hundred-fold increase in searches for the devices over other smoking alternatives such as nicotine patches between 2008 and 2010.

"It's far outpacing anything else in many parts of the world," says senior author Dr. John Brownstein, an associate professor at Harvard University.

Another U.S. study suggested that in 2012, eight per cent of people in the general population had tried an e-cigarette, an activity that's called vaping (it rhymes with taping). About a third of smokers reported having tried the devices.

With their glowing tips and exhaled mist, e-cigarettes are designed to simulate smoking. Depending on what kind of fluid cartridge -- juice in e-cigarette jargon -- they are loaded with, some deliver a hit of tobacco's addictive component, nicotine, while others use non-nicotine laced fluid in a raft of flavours including chocolate, mango and banana cream.

You might think anything that would entice or help smokers to quit would be wholeheartedly embraced by the public health field. But in this case, you would be wrong. Addiction treatment specialists, public health officials and tobacco control advocates are divided over whether e-cigarettes are useful smoking cessation aids or Big Tobacco's latest attempt to retain, regain and expand market share by getting a new generation of customers -- teenagers -- hooked on nicotine.

Should the devices, like cigarettes, be barred from restaurants, workplaces and other indoor settings? Or are they sufficiently different -- and sufficiently safe for users and the people around them -- to merit more lax regulatory treatment? Would less stringent rules for e-cigarettes "renormalize" smoking, undoing decades of anti-tobacco efforts by rendering the act of smoking -- or simulated smoking -- cool again? Will youth who start by vaping graduate to smoking cigarettes?

There are no immediate answers.

E-cigarettes are "hugely controversial," says Jessica Pepper, a doctoral candidate in health behaviour at the University of North Carolina. Pepper, who specializes in tobacco control policies, has been researching the devices.

"You have some parts of the scientific community saying 'E-cigarettes are bound to be safer than regular cigarettes so if e-cigarettes help smokers quit, we're going to be saving a ton of lives.' Then you have the other side of the debate where people are saying 'Well, what if smokers decide not to quit because e-cigarettes keep them addicted? What if smokers don't quit because they think it's OK to maybe just cut back a little on smoking and add e-cigarettes?"'

In the face of the uncertainty -- and exploding sales -- governments have been forced to respond. But the international regulatory approach to e-cigarettes resembles a patchwork quilt.

Last week New York City passed a bill that bans e-cigarette use in restaurants, bars and clubs. In the U.S., where this fall 40 state attorneys general called for tighter regulation of e-cigarettes, the Food and Drug Administration plans to treat the devices like tobacco products.

In Britain, e-cigarettes will be regulated as a medicine, which will likely set a higher bar for manufacturers seeking approval for the products. But the European Union, which had intended to regulate them as medical devices, has steered away from that path. Last week the European commission announced it will set safety and quality standards for the devices and refills, impose stricter rules on advertising and require the products to be sold with safety warnings.

Health Canada would not give The Canadian Press an on-the-record interview about how e-cigarettes are regulated in this country. But two officials involved with the file did outline the legislative lay of the land, speaking on the proviso that their names not be used.

In Canada, e-cigarettes that are sold with nicotine and/or in packaging that makes a health claim fall under the jurisdiction of the Food and Drugs Act, they say. And under that act, a manufacturer must apply to Health Canada for authorization to bring a new product to market.

A health claim might be wording that asserts that the device can help a person quit smoking or is safer to use than tobacco cigarettes.

To date, Health Canada has not approved any e-cigarettes under the Food and Drug Act, say the officials, which means that it is not legal to sell e-cigarettes with juice that contains nicotine in Canada.

Some proponents of e-cigarettes contest that assertion, suggesting e-cigarette juice containing nicotine is governed by the Consumer Chemicals and Containers Regulations of 2001.

Health Canada disagrees. "That is wrong," one of the officials declares. "Definitely nicotine is regulated under the Food and Drugs Act."

The other Health Canada official said the department has taken "hundreds" of actions related to sales of e-cigarettes and nicotine, seizing some products, writing letters to inform merchants they must stop selling the combined products and working with Canada Border Services to stop importations of products. But vapers boast online that e-cigarettes with nicotine are easy to obtain here.

Experts acknowledge that e-cigarettes may well help smokers quit. But in order to be able to claim that in marketing materials, a manufacturer would have to provide evidence generated by well-done clinical trials. And to date there isn't much in the way of data.

A study published in September suggested e-cigarettes may be slightly more effective than nicotine patches or a placebo e-cigarette (without nicotine); 7.3, 5.8 and 4.1 per cent of subjects stayed off cigarettes for six months by using those alternatives respectively. But so few people actually quit smoking that the authors could not conclude if any one method was more effective than the others.

E-cigarettes that aren't sold with nicotine or which don't make health claims can be sold legally in Canada, the Health Canada officials say. These devices are regulated under the Canada Consumer Products Safety Act, one of the officials says.

The two-pronged treatment of e-cigarettes creates the odd scenario where an e-cigarette delivering nicotine could not be advertised in Canada, but one without nicotine could be. In the United States, both kinds can be advertised, a reality the attorneys general complained about in their letter to the FDA.

"We haven't had smoking advertising ... at least in the U.S., for so long. ... It's jarring to see the commercials on TV," Pepper says.

Dr. Richard Hurt, who runs the nicotine dependence center at the Mayo Clinic in Rochester, Minn., suggests the expansion of the e-cigarette industry and market is turning back the clock on tobacco control.

"In the absence of any regulation, they're going to push the envelope as far as they can," says Hurt, who says his program won't use the devices until they've been proven to work in randomized controlled trials.

"That's the way the cigarette manufacturers did in the 50s and the 60s and the 70s until someone said 'Enough already.' And they're going to push the envelope because if they push the envelope, they're going to make more money."

But Kirsten Bell believes e-cigarettes ought to be given a chance.

A professor of anthropology at the University of British Columbia, Bell has researched the public health responses to the devices. She feels e-cigarettes aren't being given a fair shot.

"They were sort of being condemned without trial by the majority of people in mainstream tobacco control in public health," Bell says.

"You have this sort of unquestioning extension of smoke-free legislation to cover e-cigarettes when of course an e-cigarette isn't a cigarette. It's not a combustible product."

She thinks there's a sort of moralistic agenda at play, one that equates nicotine use with smoking, even though the dangers of cigarettes relate to how they deliver nicotine, not the compound itself.

"I'm not sure that I buy this idea that because you see people vaping e-cigarettes it's going to make you go out and try cigarettes," Bell says.

"I don't think that they will renormalize smoking. But if they do normalize vaping, that would only be a problem really if vaping itself is something that is harmful. And at the moment, we don't have the answer to that question."