When e-cigarettes were introduced to the U.S. market in 2007, they were billed as a safe alternative to conventional tobacco cigarettes. But since then, vaping has been linked to a mysterious lung disease that has sickened hundred of people around the country, causing several deaths. Various studies have found that these e-cigs may not be so harmless after all, and local and state governments are taking action.

Many e-cigarettes are designed to look like conventional cigarettes, but they are actually battery-operated devices. They contain an atomizer that heats a nicotine liquid, which turns to vapor; the vapor is then inhaled and exhaled, much like tobacco smoke.

The liquid — commonly known as e-juice, e-liquid, smoke juice and cig juice — comes in a cartridge and is a mixture of nicotine, water, glycerol, propylene glycol and flavorings, according to the Tobacco Vapor Electronic Cigarette Association.

The amount of nicotine varies; consumers can select cartridges ranging in strength comparable to ultralight cigarettes all the way to regular-strength smokes.

And yes, the liquid comes in flavors. Although e-cigarette manufactures say they don't market to young people, liquid cartridges come in a nauseating array of flavors — everything from butterscotch and fruit punch to cinnamon bun and milkshake.

The federal government as well as several states have pushed legislation to ban most flavored e-cigarettes because they appeal to young people.

vaping products, candy names, ban in San Francisco The names of vaping products run the gamut, but many look more like new flavors of bubblegum than smoking products. (Photo: Justin Sullivan/Getty Images)

Vaping health concerns

This summer, the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) joined forces to investigate severe lung illnesses that the agencies believe are linked to e-cigarette use.

This isn’t the first time that vaping has come under the microscope.

Researchers have found that almost all e-cigarette vapor contains two cancer-causing chemicals: propylene glycol and glycerin. The study was published in the journal Environmental Science and Technology.

"Advocates of e-cigarettes say emissions are much lower than from conventional cigarettes, so you're better off using e-cigarettes," said Berkeley Lab researcher and the study's corresponding author Hugo Destaillats, in a statement. "I would say, that may be true for certain users — for example, long time smokers that cannot quit — but the problem is, it doesn't mean that they're healthy. Regular cigarettes are super unhealthy. E-cigarettes are just unhealthy."

Previous reports have also found health concerns with e-cigarettes. A report published in the New England Journal of Medicine found that e-cigs give off formaldehyde, which is another carcinogen. And in 2009, the FDA announced that a laboratory analysis of electronic cigarette samples found that they contain "carcinogens and toxic chemicals such as diethylene glycol, an ingredient used in antifreeze."

Despite these dangers, people are still lighting up electronically. About 15.4% of all adults (and 23.5% of adults 18 to 24) used e-cigarettes in 2016, according to a CDC report. E-cigarettes have been the most commonly used tobacco product among U.S. youth since 2014, says the CDC, with one in five high school students and one in 20 middle school students using e-cigarettes in 2018.

In an interview with the Washington Post, U.S. Surgeon General Vivek H. Murthy called the increasing number of young people using e-cigarettes a "major public health concern."

"We know enough right now to say that youth and young adults should not be using e-cigarettes or any other tobacco product, for that matter," Murthy said. "The key bottom line here is that the science tells us the use of nicotine-containing products by youth, including e-cigarettes, is unsafe."

There may be one small silver lining in this cloud. A study published in the British Medical Journal found that e-cigarettes may have helped more people quit smoking. Researchers found that the number of people trying to quit didn't change, but the number of successful attempts increased. About 18,000 additional people kicked the habit in the U.K. in 2015, the study found.

Editor's note: This story has been updated since it was originally published in November 2015.

What are e-cigarettes?
Electronic cigarettes are surging in popularity among young people, despite bans in Michigan and San Francisco.