Good news for vapers who aren’t keen on sucking back a chemical widely used in embalming fluid: e-cigarettes don't appear to emit as much formaldehyde as previously thought, and tend to emit levels much lower than cigarettes, according to a study published this week in Regulatory Toxicology and Pharmacology.

The study was a kind of rebuttal to a controversial letter published in the New England Journal of Medicine last year that raised alarm bells about dangerously high levels of formaldehyde in e-cigarette vapor. The letter outlined a test the authors had done to measure the levels of formaldehyde (a known carcinogen) emitted from an e-cigarette, writing that the device tested puffed out as much as five times the formaldehyde as cigarettes when on the highest heat setting. The authors even concluded that vapers were at as much as 15 times higher risk of cancer than smokers.

Many scientists took umbrage with this letter, highlighting some flaws in the methodology and conclusion. More than 40 researchers and experts backed a plea to have the letter retracted. Part of the criticism circled around the fact that the researchers had only detected these high formaldehyde emissions when the vaporizer was cranked to a very high voltage level. When vaporizers heat up that quickly, they rip through juice too fast, dry out, and create a nasty taste. It’s so noticeable that vapers even have a name for it, a “dry puff” or “dry hit,” and try to avoid it. (Seriously, one Redditor described it as “burnt hair flavor” and described a desperate attempt to get the taste out of his or her throat after a single hit.)

Another criticism was with lumping all devices in under the results from testing just one type of vaporizer.

“There needs to be context because the term ‘electronic cigarette’ is not just one thing,” said Kurt Kistler, a chemistry professor at Penn State and co-author of the new study. “E-cigarettes include a huge variety of devices, power settings, wattage control, voltage control, and even temperature control.”

Rather than just write a letter, Kistler decided to just do the same experiment himself to see if he could recreate the findings, the results of which are what was published this week.

Kistler worked with a team of researchers at Enthalpy Analytical, a lab in North Carolina that focuses on e-liquid testing, to analyze the vapor of five different refillable e-cigarette devices for the presence of three different aldehydes: formaldehyde, acetaldehyde, and acrolein, all of which are known to emerge when mixtures of glycerol and propylene glycol (the main ingredients in e-liquids) are heated. These chemicals are some of the laundry list of nasty emissions produced by cigarettes. Formaldehyde is considered a carcinogen, acetaldehyde is considered a possible carcinogen, and acrolein can cause lung damage. They’re not something you want to be inhaling regularly.

Kistler and his team found that the levels emitted varied widely depending on the device and the power used, but that most levels were far below what smokers inhale. Even at the highest power settings, three of the five devices produced formaldehyde, acetaldehyde, and acrolein levels of less than 1 milligram each per day. In contrast, smoking a pack of cigarettes in a day exposes a smoker to 1.5-2.5 mg of formaldehyde, 10-30 mg of acetaldehyde, and 1.5-3 mg of acrolein. The levels emitted by those three e-cigarettes were also well below the exposure limits for these chemicals outlined by the Occupational Safety and Health Administration.

One of the other two devices started to produce higher levels of formaldehyde and acetaldehyde at its two highest power settings, and the other had consistently high levels of both of these compounds throughout the test. In fact, the one device was consistently emitting levels higher than cigarettes, in some cases as high as 20 times higher.

However, the researchers had a theory for why that may have been the case: the coil (the part of the device that distributes heat to the e-juice) could have become overheated after using up all the liquid, causing dry puff. Previous studies have shown vaporizers with overheated coils can lead to high emissions of aldehydes. After the study was done, the researchers noticed the coil was charred, which backs up their theory, though they can’t be sure this is what happened. Still, the possibility is important to point out because dry puff is so gross, it’s unlikely any vaper would use a device at that level.

“Dry puff is noxious,” Kistler said. “It burns the nose. It burns the throat. It’s very, very unpleasant. No vaper is going to just sit there and inhale that. It kind of forces the vaper to just shut it off entirely.”

Of course, five devices don’t represent the entirety of the vast e-cigarette industry. There are countless other models, customizations, and other variables like flavorings (the researchers used unflavored liquid in this study) that could result in different emissions. Kistler readily acknowledged there’s more work to do, but said he wanted to establish the need to include the context of user habits and device variability when studying the health risks of vaping.

“We wanted to get a baseline and give people the information that these early studies were not the end of the story whatsoever,” Kistler said.


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