Advocates tout the e-cigarette as a clean alternative to old-fashioned tobacco, one that can even help people quit smoking. But although the companies making these largely unregulated products promote e-cigarettes as safe and pure, the reality is a little more complicated. Here are four common misconceptions about e-cigarettes, and the scientific evidence against them.

Myth 1: Vapor from e-cigs is pure.

The liquid "vaped" in an e-cigarette contains nicotine, water and a solvent (usually glycerine or polyethylene glycol). It may also contain flavoring agents, such as oil of wintergreen. Although this mixture may sound pure enough, neither the liquid (called the e-liquid) nor the device's delivery system are regulated; this means e-cigarettes could produce harmful chemicals.

In fact, recent studies have identified impurities ranging from formaldehyde to heavy metals in e-cig vapor. And vaporized polyethylene glycol is a known eye and respiratory irritant.

One recent study found formaldehyde, acetaldehyde and acetone in the vapor of several different e-cigarette models and liquid nicotine products found formaldehyde, acetaldehyde and acetone. "We found nicotine, of course, but we also found some potentially dangerous compounds," said study researcher Maciej Goniewicz, an assistant professor of oncology at Roswell Park Cancer Center in Buffalo, New York.

What's more, users can amp up the voltage of an e-cig delivery device, resulting in a denser, more nicotine-rich vapor. Goniewicz and his team found that at a higher voltage and hotter temperature, levels of harmful chemicals increased, too.

The vapor had a lower chemical content than tobacco smoke, but there was "huge variability" among the products tested, Goniewicz told Live Science. "It doesn't mean that each product will expose users to high levels of formaldehyde, but there is a risk for sure," he said.

Myth 2: E-cigs are safe.

In addition to potential toxicity from chemical byproducts, which could harm users over the long term, e-cigs carry another safety risk. Liquid nicotine is extremely toxic when swallowed, and in some case reports, infants and children have accidentally ingested the substance.

Story continues

The chances of this happening may increase with flavored liquid nicotine, which may come in enticing-looking packages and can smell tempting, according to new research.

"It mistakenly has this reputation for being safe because it's purchased over the counter, but it easily can be fatal if it's taken in high doses," said Dr. Robert A. Bassett, a medical toxicologist and emergency medicine physician at Einstein Medical Center in Philadelphia. Bassett and his colleagues reported a case of liquid nicotine poisoning in a 10-month-old infant in the May 7 issue of JAMA.

The boy recovered within a few hours, but nicotine poisoning could easily be fatal, Bassett said. A teaspoon of standard liquid nicotine would be enough to kill a person who weighs 200 pounds (90 kilograms), Bassett and his colleagues noted in their report.

Myth 3: E-cigs can help you quit smoking.

The few studies looking at whether or not using e-cigs helps people kick the habit have had mixed results. Some studies have found people who tried e-cigs wound up smoking fewer regular cigarettes, but they were no more likely to give up smoking entirely.

Overall, the authors of a recent scientific review conclude, "studies that reflect real-world e-cigarette use found that e-cigarette use is not associated with successful quitting ... Taken together, the studies suggest that e-cigarettes are not associated with successful quitting in general population-based samples of smokers." [Kick the Habit: 10 Scientific Quit-Smoking Tips]

And there is even some evidence that e-cigs may get non-smokers hooked on nicotine. Studies have found as many as one-third of young e-cigarette users have never tried conventional cigarettes.

Myth 4: E-cigs don't produce harmful second-hand smoke.

A main selling point of e-cigs is that they can be used anywhere, because they don't produce toxic smoke that puts others at risk. But breathing in second-hand vapor, also known as "passive vaping," may not be harmless. In fact, experts say although The level of toxic chemicals in second-hand vapor is smaller than that in second-hand smoke. But experts say e-cig smoke contains a similar amount of tiny particles of heavy metals and other substances that can damage the lungs.

The Food and Drug Administration has proposed a rule that would permit the agency to regulate e-cigarettes and similarproducts. If the proposal becomes final, the agency said, it will be able to use regulatory tools, such as age restrictions and rigorous scientific review of new tobacco products and claims to reduce tobacco-related disease and death.

Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

Copyright 2014 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.