What’s in Your E-Cigarette?

From the WebMD Archives

Feb. 18, 2015 -- As the popularity of electronic cigarettes has grown over the past several years, so have concerns over the health risks tied to them.

The New England Journal of Medicine, for example, recently published a letter from researchers that set off alarm bells. They reported that some e-cigarettes release formaldehyde, a probable cancer-causing substance (or carcinogen), when heated with batteries set at high voltages. 

On Jan. 28, the California State Department of Public Health released a report declaring e-cigarettes a public health threat and calling for regulation.

So, What’s in E-cigarettes?

That’s not an easy question to answer. No federal agency oversees the e-cigarette industry. That means no standards exist. Labels may inaccurately describe ingredients, and what you find in one brand may be vastly different from that found in another, for better or worse.

The results of one FDA review of 18 different e-cigarette cartridges found toxic and carcinogenic chemicals in some but not others. All but one of the cartridges labeled “no nicotine” did, in fact, contain nicotine. The authors suggest that “quality control processes used to manufacture these products are inconsistent or non-existent.”

Here’s some of what we do know.

The E-Liquid

E-liquid, or e-juice, is the name for the solution that’s heated up and converted to an aerosol, which e-cigarette users inhale. Here are its most common ingredients:

Nicotine: The addictive ingredient in e-cigarettes and regular cigarettes, nicotine stimulates the central nervous system and raises blood pressure, respiration, and heart rate. “People smoke because of the nicotine,” says researcher Maciej Goniewicz, PhD, PharmD. He's a tobacco and e-cigarette expert at the Roswell Park Cancer Institute in Buffalo, N.Y.

While it's addictive, nicotine doesn't cause cancer, says Goniewicz: “What causes concern are the other chemicals (in the e-liquid).”

Flavorings: Goniewicz says hundreds of flavors exist, including cherry, cheesecake, cinnamon, and tobacco. Many of those flavoring chemicals, he says, are also used to flavor food.

“These are the big unknowns,” he says. “When we eat them, they are safe, but we don’t know what’s going on when we inhale them.”


It would be impossible to list all the various flavoring chemicals here, but one such chemical, diacetyl, is commonly used to add buttery flavor to popcorn. It's been linked to obstructive lung disease when inhaled. Other chemicals that add buttery flavor might be harmful as well, says Neal Benowitz, MD. He's a former member of the FDA’s Tobacco Products Scientific Advisory Committee.

Propylene glycol (PG): PG is a lab-made liquid that the FDA generally views as safe in food, drugs, and cosmetics. It's also used to make artificial smoke or fog for rock concerts and other performances. It can irritate the lungs and eyes and may be more harmful for people with chronic lung diseases like asthma and emphysema.

Glycerin: Odorless and colorless, liquid glycerin has a slightly sweet taste. Like PG, the FDA generally views it as safe. It’s found in many products, including food and drugs, both prescription and over the counter.

While both PG and glycerin are safe in food and drugs, Goniewicz says, “we don’t know what happens if someone inhales large amounts of these chemicals over the long term. This is really unknown.”

Heating Up

Toxic chemicals are formed as the e-liquid heats up to make the aerosol that e-cig users inhale. Some of these chemicals can cause inflammation and blood vessel damage responses, says Benowitz, who's also a professor at the University of California, San Francisco's School of Medicine. “In most preparations, they are much lower than you find in cigarette smoking, but they are of concern, no question about it,” he says.

Those chemicals include:

Formaldehyde: A probable carcinogen.

Acetaldehyde: Another probable carcinogen.

Acrolein: Formed from heated glycerin, acrolein can damage the lungs and contribute to heart disease in smokers.

All three are released in increasing amounts as the temperature of the e-liquid rises. And, says Benowitz, users may be tempted to go for those higher temperatures.

“Unfortunately, the higher you heat the liquid, the more nicotine you get from it,” he says. “People who want to get a big dose of nicotine may use really high voltage batteries or an adjustable voltage battery.”

Goniewicz says flavors might mask the unpleasant taste that results when users heat their e-cigarettes to the point at which formaldehyde is made.


Particulates and Metals

The tiny particles in e-cigarette aerosol also may be harmful. This is certainly the case for cigarette smoke and other air pollution, which can cause blood vessel damage, inflammation, and nervous system effects, Benowitz says.

E-cigarette aerosol has similar levels of particulates as regular cigarettes. But not enough research has been done on e-cigarettes to draw any conclusions about the safety of breathing in the particles they produce.

Toxic metals such as tin, nickel, cadmium, lead, and mercury have been found in e-cigarette aerosol, too. A 2013 study notes that some metals, such as nickel, occur in concentrations 2 to 100 times that of cigarettes.

Are E-Cigarettes Safe?

“It’s all relative to cigarette smoking,” Benowitz says. “Based on what we know now, they are much less hazardous than regular cigarettes.”

And regular cigarettes, as everyone should know, are truly bad for you. According to the American Lung Association, cigarettes give off about 7,000 chemicals when burned, many of them poisonous -- at least 69 of those chemicals cause cancer.

E-cigarettes do appear to be less dangerous for those exposed to secondhand aerosol. E-cigarette users exhale very little of what they breathe in, says Benowitz, and their devices emit no aerosol. Cigarettes, by contrast, pollute the atmosphere and others’ lungs at a very high rate.

“Seventy-five percent of the smoke generated by cigarettes is sidestream smoke, and that goes into the environment,” Benowitz says.

Still, much more research needs to be done to fully figure out the health risks that e-cigarettes pose for both users and bystanders.

Both Benowitz and Goniewicz say e-cigarettes may prove helpful to smokers who are trying to quit. But that's another issue that needs much more study.

And for people who don’t already smoke?

“This is not a product for non-smokers,” Goniewicz says. “If you are not a smoker, don’t use it. There’s no reason to try electronic cigarettes.” The nicotine is addictive.

WebMD Health News Reviewed by Arefa Cassoobhoy, MD, MPH on February 18, 2015



Maciej Goniewicz, PhD, PharmD, assistant professor of oncology, department of health behavior, Roswell Park Cancer Institute, Buffalo, N.Y.

Neal Benowitz, MD, professor, University of California San Francisco School of Medicine, San Francisco, CA.

Luo, W. New England Journal of Medicine, Jan. 22, 2015.

National Institute on Drug Abuse. “DrugFacts: Cigarettes and Other Tobacco Products.”

Grana, R. Circulation, 2014.

Goniewicz, M. Tobacco Control, March 2013.

Agency for Toxic Substances and Disease Registry: “Propylene Glycol."

Dow Chemicals: “Product Safety Assessment: Glycerin."

National Cancer Institute: “Formaldehyde and Cancer Risk."

EPA: “Acetaldehyde.”

American Lung Association: “What’s in a Cigarette?”

FDA: “Summary of Results: Laboratory Analysis of Electronic Cigarettes Conducted By FDA.”

California Department of Public Health: “Health Advisory - Jan. 28, 2015."

Williams, M. PLOS One, March 2013.

© 2015 WebMD, LLC. All rights reserved.