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 various studies have found that these e-cigs may not be so harmless after all, and local and state governments are taking action.

Researchers 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."

Currently, the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) are investigating a "cluster" of severe lung illnesses that the agencies believe may be linked to e-cigarette use. Since Sept. 12, the CDC is focusing on 380 likely or confirmed cases in 36 states and 1 U.S. territory, instead of the more than 450 “possible” illnesses it was reviewing earlier. At least six people have now died from the illness in California, Illinois, Indiana, Minnesota, Oregon and Kansas.

The CDC urged Americans to stop using e-cigarettes during the investigation.

"While this investigation is ongoing, people should consider not using e-cigarette products. People who do use e-cigarette products should monitor themselves for symptoms (e.g., cough, shortness of breath, chest pain, nausea, vomiting, abdominal pain, fever) and promptly seek medical attention for any health concerns," said the CDC in a statement.

The agencies are investigating the exact cause and whether the illnesses are linked to a specific devices, ingredients or contaminants. Presently, the cases don't appear to be linked to one product, the agencies said, although they noted that in "many" cases, patients had reported using THC and other compounds found in cannabis.

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-cigarette 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 2016 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.

E-cigarette sales in the U.S. reached $3.7 billion in 2015, and analysts predict that sales could hit $10 billion in five years.

How e-cigarettes work

man vaping in a cloud of smoke E-cigarettes have an atomizer that heats a nicotine liquid that turns to vapor. (Photo: PavelKant/Shutterstock)

Many of them are designed to look like conventional cigarettes, but they are actually battery-operated devices. They contain an atomizer that heats a nicotine liquid that 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 laws around e-cigs

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)

The Trump administration announced in mid-September that it would ban the sale of most flavored e-cigarettes. The ban, which is expected to take several weeks to enact, would include mint and menthol, which are popular with young people.

Michigan became the first state to ban flavored e-cigarettes. The blanket ban went into effect on Sept. 4. State officials are particularly worried about vaping by young people, calling it a public health emergency. Gov. Gretchen Whitmer called out the companies selling vaping products aimed at children — potentially hooking them on nicotine early with candy-inspired product names and creating a lifetime habit.

On Sept. 15, New York Gov. Andrew Cuomo announced an emergency executive action to ban the sale of flavored e-cigarettes in the state. It's expected to go into effect in about two weeks. The state will also be cracking down on stores that sell to underage youth, with the possibility of criminal penalties.

San Francisco became the first city to ban e-cig sales after city officials voted June 26 to ban stores from selling the items and online retailers from delivering to city addresses, according to CNN. Mayor London Breed' signed the ordinance a few days later.

San Francisco's ban is notable not only for the city's early action but also because it's home to leading e-cigarette manufacturer Juul Labs.

The actions highlight what e-cigarette opponents and health advocates say is the FDA's failure to act on the issue, points out CNN. Officials from San Francisco, New York and Chicago criticized the FDA in a March letter for allowing e-cigs to remain for sale without undergoing a review on their impact on public health.

"San Francisco has never been afraid to lead and we're certainly not afraid to do so when the health and lives of our children are at stake," City Attorney Dennis Herrera said in that letter. "By law, before a new tobacco product goes to market, the Food and Drug Administration is supposed to conduct a review to evaluate its impact on public health. Inexplicably, the FDA has failed to do its job when it comes to e-cigarettes. Until the FDA does so, San Francisco has to step up."

The Food and Drug Administration banned e-cig sales to children under 18 in May 2016, but other regulation has been slippery. According to the FDA, currently e-cigarettes that are marketed for therapeutic purposes (like the cessation of smoking) are regulated by the FDA Center for Drug Evaluation and Research (CDER). The FDA finalized a rule that went into effect in August 2016 that broadens the administration's authority to include e-cigarettes.

The FDA has stated its intent to issue a proposed rule that would extend the agency's authority to products that meet the statutory definition of "tobacco product," which would include e-cigarettes.

"Before this final rule, these products could be sold without any review of their ingredients, how they were made, and their potential dangers," explains Mitch Zeller, J.D., director of the FDA's Center for Tobacco Products, in a statement. "Under this new rule, we're taking steps to protect Americans from the dangers of tobacco products, ensure these tobacco products have health warnings, and restrict sales to minors."

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

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