In this Feb. 20, 2014 photo, a patron exhales vapor from an e-cigarette at the Henley Vaporium in New York. the proprietors are peddling e-cigarettes to "vapers" in a growing movement that now includes celebrity fans and YouTube gurus, online forums and vapefests around the world. (AP Photo/Frank Franklin II)

Those colorfully lit e-cigarettes are giving off way more than just "harmless water vapor," according to a comprehensive new study review by UC San Francisco's Center for Tobacco Control Research and Education. Users could also be inhaling and exhaling low levels of chemicals such as formaldehyde, propylene glycol and acetaldehyde (to name a few), and this secondhand vapor could be a potentially toxic source of indoor air pollution.

While the levels of the toxins were still much lower compared to conventional cigarette emissions, the findings fly in the face of the e-cigarette industries' claims that the handheld devices are just as safe as any other smoking cessation tool.

E-cigarettes as we know them today were invented by a Chinese pharmacist, Hon Lik in the early 2000s as a smoking cessation aid. They are handheld nicotine vaporizers that deliver an aerosol made up of nicotine, flavorings and other chemicals to users. It's the chemicals in those vapors that are moving municipalities like Los Angeles, New York City, Washington D.C., Chicago and Boston to restrict "vaping" in some way.

Formaldehyde, for instance, is a carcinogen that also irritates the eyes, nose and throat. Propylene glycol can also cause eye and respiratory irritation, and prolonged exposure can affect the nervous system and the spleen. Acetaldehyde, also known as the "hangover chemical," is also a possible carcinogen.

The secondhand vapor finding is just one of several that UCSF researchers highlighted in the broadest review to date of peer-reviewed e-cigarette studies. The findings, which were published Monday in the American Heart Association's journal Circulation, include:

1. Some youth have their first taste of nicotine via e-cigarettes. Twenty percent of middle schoolers and 7.2 percent of high schooler e-cigarette users in the U.S. report never smoking cigarettes.

2. Nicotine absorption varies too much between brands. Early 2010 studies found that users got much lower levels of nicotine from e-cigarettes than from conventional cigarettes, but more recent studies show that experienced e-cigarette users can draw levels of nicotine from an e-cigarette that are similar to conventional cigarettes. Yet another study noted that the chosen e-cigarettes for the research malfunctioned for a third of participants. UCSF researchers say this indicates the need for stronger product standards and regulations.

3. Just because particulate matter from e-cigarettes isn't well studied, doesn't mean it's safe. To deliver nicotine, e-cigarettes create a spray of very fine particles that have yet to be studied in depth. "It is not clear whether the ultra-fine particles delivered by e-cigarettes have health effects and toxicity similar to the ambient fine particles generated by conventional cigarette smoke or secondhand smoke," wrote the researchers. But we do know that fine particulate matter from cigarettes and from air pollution are associated with an increased risk of cardiovascular and respiratory disease. And some research has found that the size and spray of fine particulate matter from e-cigarettes is just as great or greater than conventional cigarettes.

4. So far, e-cigarette use is not associated with the successful quitting of conventional cigarettes. One clinical trial found that e-cigarettes was no more effective than the nicotine patch at helping people quit, and both cessation methods "produced very modest quit rates without counseling."

5. Major tobacco companies have acquired or produced their own e-cigarette products. They're promoting the products as "harm reduction" for smokers, which allows them to protect their cigarette market while promoting a new product. Companies also using "grassroots" tactics to form seemingly independent smokers' rights groups, just like they did for cigarettes in the 1980s.