E-cigs create toxic vapors from harmless e-liquids

And with increasing use, electronic cigarettes become richer sources of these toxic chemicals
Jul 28, 2016 — 12:00 pm EST
girl vaping

Girl vaping on an e-cigarette. The cloud of gases these devices emit can contain toxic chemicals. Which chemicals and how much depends on how the device is used and the solvent used in the e-liquids, new data show.


Some people think electronic cigarettes, which don’t contain tobacco, are a safer alternative to true cigarettes. But smoking e-cigarettes, or vaping, exposes people to toxic gases that can harm the lungs and cause other health problems. Now, a new study shows that the hotter an e-cig gets — and the more it’s used — the more toxic compounds it gives off.

Hugo Destaillats is a chemist at Lawrence Berkeley National Laboratory in California. His team has just turned up a host of toxic chemicals in the vapors generated by electronic cigarettes. Some have never before been seen in vaping emissions. “There is this image that e-cigarettes are a lot better than regular cigarettes, if not harmless,” Destaillats says. As a result of the new research, he says, “We are now definitely convinced that they are far from harmless.” 

Key to vaping is the e-liquid that is drawn through an e-cigarette. Manufacturers dissolve flavorings, and usually nicotine, into this solvent. In most cases, this solvent is known as food-grade, meaning it should be safe enough to eat. (But that rating is meaningless if the solvent will be inhaled into the lungs, not ingested into the stomach, where it can break down.)

As a vaper inhales, some of the flavored solvent will flow through the e-cigarette. As it passes over one or more hot metal coils, that liquid vaporizes into a gas.

These flavored vapors can be a rich source of toxic chemicals. One of those toxic chemicals is nicotine. It is usually added to the starting liquid to stimulate a user's nervous system the same way that tobacco cigarettes will. (Indeed, e-cigs are considered "tobacco products" by government agencies because their nicotine comes from tobacco plants. ) But the new study finds that the solvents make even more chemicals that are bad to breathe in.  As the solvents encounter an e-cig’s intensely hot coil, they can break down to form new toxic compounds.

Those chemicals include formaldehyde (For-MAL-duh-hyde) and acetaldehyde (AA-sit-AL-duh-hyde). Both are considered likely to cause cancer. Another toxic aldehyde — acrolein (Aa-KRO-LEE-un) — can severely irritate the eyes and airways.

The Berkeley team used two current types of e-cigs and three different e-liquids. Their test equipment mechanically drew air through the electronic devices. This created vapors that a user would normally inhale. The chemicals making up those vapors changed as the e-cigs heated up. That means the first puffs contained somewhat less of the toxic chemicals than later puffs did.

Some e-cigs, such as ones they used in these tests, allow a user to vary the voltage (battery power used to heat the metal coils). Higher voltages produced hotter coils and more of the toxic chemicals.

The team presented its data July 27 in Environmental Science & Technology.

The role of heat and dirty ‘gunk’

The bottles of e-liquids used in the new tests came from the store with tiny traces of aldehydes, Destaillats notes. But the levels were too low to matter. However, he reports, “through the process of vaping, you are generating almost 1,000-fold higher emissions of those same compounds.”

vapors graph
E-cigarettes with higher voltage produce more toxic aldehydes per puff. Once an e-cig reaches a high voltage, each further increase causes an extra-large jump in three of the most harmful compounds in the vapor (see last bar).

What seems to be happening, he says, is that the more heat you pour into the e-cigarette, the faster it makes the liquid evaporate. At some point, however, the liquid can’t get any hotter. So putting even more heat into it no longer just vaporizes it. Now the liquid actually breaks down into new, and more toxic, chemicals.

That increase in the formation of toxic gases tended to climb gradually as the coils got hotter. But at high voltages that changed. Suddenly, Destaillats notes, there was a sharp boost in the three most harmful aldehydes present in the vapor.

In most of their tests, the chemists used a new e-cigarette for each puffing session. But for one set of tests, they used the same device over and over. They also set it at a high-voltage level. After the ninth 50-puff cycle, they compared the vapors coming out to those from the first few puffs. And the vapors were different. The later ones contained 60 percent more aldehydes than the first few puffs had.

This effect matched what would be expected if there was a chemical buildup on or near the heating element, the scientists say. As e-liquids break down, they will leave some residues behind. The slang term for this stuff is “coil gunk.” These residues, the Berkeley scientists now say, would serve as an additional source of material from which to make toxic aldehydes.

What’s new here

Realizing there are changes in the vapors of well-used e-cigarettes “is something new,” notes Maciej Goniewicz. He’s a toxicologist at the Roswell Park Cancer Institute in Buffalo, N.Y. He also has studied the role of e-cigarette types and power levels on aldehyde production.

The Berkeley team used a better analytical technique than others have employed, including his group, Goniewicz says. And with this new technique, the Berkeley team turned up new compounds in the vapors, he points out. These include propylene oxide and glycidol. Both are toxic, he notes. Neither his group nor others had previously been able to see these in e-cig vapors.

Studies such as the new one are important, he says, “because they will help us understand exactly what people are inhaling.”

Such data also can point out ways to vape more safely, argues Destaillats. “In a way,” he says, “the message to people using e-cigarettes is: If you’re going to vape, try using the lowest voltage possible, for the lowest temperature.”

But in no circumstances should teens be vaping, he notes. Yet data show that plenty do. And access to these potentially dangerous products has been fairly simple. Although most U.S. states have made it illegal for teens to buy vaping goods, these supplies could still be ordered over the internet.

That could change soon. In May, the U.S. Food and Drug Administration said vaping products would be treated no differently than cigarettes and other tobacco products in terms of young people. It will violate federal law to sell or give vaping products to U.S. minors.

Power Words

(for more about Power Words, click here)

acetaldehyde    A colorless liquid that is in the cascade of breakdown products that develops when the body metabolizes alcohol. The colorless liquid also is used by manufacturers to make a range of products, including vinegar, perfume and flavorings. According to the U.S. National Toxicology Program, this chemical is also “reasonably anticipated to be a human carcinogen.”

acrolein    A liquid that’s clear or yellowy and has an odor that can create a choking sensation. In high concentrations it’s a known poison. Manufacturers add it to plastics, medicines, pesticides, resins and more.

aldehyde    A family of chemicals that can be formed by the oxidation of alcohols. These compounds, known as organic (because they contains carbon) contain a chemical group: CHO. Many members of this family, notably formaldehyde, are toxic.

cancer   Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

chemical   A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

e-cigarette    (short for electronic cigarette) Battery-powered device that disperse nicotine and  other chemicals as tiny airborne particles that users can inhale. They were originally developed as a safer alternative to cigarettes that users could use as they tried to slowly break their addiction to the nicotine in tobacco products.

e-liquid    A term for the solutions heated to the evaporation point in an electronic cigarette. These solutions are the basis of the vapors that will be inhaled. The liquid typically contains a solvent into which flavorings and nicotine have been dissolved.

formaldehyde   A widely used and toxic chemical that manufacturers add to plastics, resins, some fertilizers, dyes, medicines and embalming fluids. It’s even in the treatments used to keep fabrics from wrinkling.

minors    Children and adolescents below an age that would make them legally adults.

nicotine    A colorless, oily chemical produced in tobacco and certain other plants. It creates the ‘buzz’ effect associated with smoking. It also is highly addictive, making it hard for smokers to give us their use of cigarettes. The chemical is also a poison, sometimes used as a pesticide to kill insects and even some invasive snakes or frogs.

solvent    A material (usually a liquid) used to dissolve some other material into a solution.

tobacco    A plant cultivated for its leaves. Dried tobacco leaves are burned in cigars, cigarettes, and pipes. Tobacco leaves are also sometimes chewed. The main constituent of tobacco leaves is nicotine.

toxic    Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

toxicology    The branch of science that probes poisons and how they disrupt the health of people and other organisms. Scientists who work in this field are called toxicologists.

vaping    (v. to vape) A slang term for the use of e-cigarettes because these devices emit vapor, not smoke. People who do this are referred to as vapers.

vaporize   To convert from a liquid to a gas (or vapor) through the application of heat.

vapors    Fumes released when a liquid transforms to a gas, usually as a result of heating.

voltage   A force associated with an electric current that is measured in units known as volts. Power companies use high-voltage to move electric power over long distances.


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M. Sleiman et al. Emissions from electronic cigarettes: Key parameters affecting the release of harmful chemicalsEnvironmental Science & Technology. Published online July 27, 2016.

J.L. Barrington-Trimis et al. E-cigarettes and future cigarette usePediatrics. Vol. 138, July 2016, p. e20160379. doi: 10.1542/peds.2016-0379.

U.S. Food and Drug Administration. Deeming Tobacco Products to be Subject to the Food, Drug, and Cosmetic Act, as Amended by the Family Smoking Prevention and Tobacco Control Act; Regulations Restricting the Sale and Distribution of Tobacco Products and Required Warning Statements for Tobacco Product Packages and Advertisements. May 2016.

L. Kosmider et al. Carbonyl compounds in electronic cigarette vapors: Effects of nicotine solvent and battery output voltageNicotine & Tobacco Research. Vol. 10, October 2014, p. 1319. doi: 10.1093/ntr/ntu078.

Further Reading

M. Rosen and J. Raloff. “Vaping can lead to teen smoking, new study finds.” Science News for Students. August 19, 2015.

J. Raloff. “E-cigarettes lower immunity to flu and other germs.” Science News. February 4, 2015.

J. Raloff. “E-cigarettes may inflame lungs as much as cigarettes do.” Science News. Vol. 186, July 12, 2014, p. 20.

J. Raloff. E-cigarettes proving to be a danger to teensScience News. June 30, 2015.