High levels of cancer-causing chemical found in mint and menthol e-cigarettes: Study A cancer-causing chemical was found in some e-cigarette liquids.

The Food and Drug Administration has announced plans to ban all non-tobacco flavored e-cigarettes and now a study from Duke University raises serious health concerns for people using mint and menthol flavored e-cigarette products: a potentially cancer-causing chemical in some of the e-cigarette liquids.

The study details high levels of a chemical called pulegone, which in other studies has been found to cause cancerous changes in the livers and lungs of mice that ingested it. Pulegone is a constituent of oil extracts prepared from mint products and it’s been found in mint and menthol-flavored e-cigarette products.

The researchers used previously published Centers for Disease Control data of the concentrations of pulegone in select e-cigarette liquids -- and also in smokeless tobacco -- and combined these with the ingestion exposure data from animal studies to calculate a “margin of exposure,” a level used by regulatory agencies including the FDA to assess human health risks. Theoretically, the larger the safety margin, the safer the product.

“We found that for all mint and menthol liquids that we analyzed, the range was 300-6,000, where levels should be at least above 10,000,” Dr. Sairam Jabba, Senior Research Associate at Duke University and co-author of the study, told ABC News.

The data was originally collected in 2015 at a time when many vaping devices involved larger volume tank systems, refilled by users with separately purchased oil, rather than the more ubiquitous smaller volume pods we see today. Brands evaluated by the study included V2 -- a company later purchased by JUUL -- as well as Premium, South Beach Smoke and Skoal mint snuff.

“Now in 2019, there is still a large number of tank users, often the most regular and intense users of vaping products and likely at the highest risk of developing adverse reactions,” explains Dr. Sven-Eric Jordt, study co-author.

Because of its potential cancer-causing properties, the FDA banned pulegone as a food additive last year in response to petitions from consumer groups. The tobacco industry has been aware of pulegone’s cancer-causing potential and has made efforts to reduce levels in menthol cigarettes.

However, in the studied mint and menthol e-cigarette liquids, the estimated pulegone exposure is significantly higher than exposure from cigarettes, according to the study’s authors.

As of now, the FDA has not regulated the chemical’s presence in e-cigarettes and smokeless tobacco, which have been promoted as safer alternatives to regular cigarettes.

“Current regulations on e-cigarettes are inadequate,” Jabba said. “The FDA needs to implement new regulations to exclude harmful chemicals like pulegone to reduce the associated health effects.” All companies were contacted for comment about pulegone concentrations in their products and only Premium responded.

“Oral absorption and ingesting are not interchangeable for this method,” Vitali Servutas, the CEO of Premium, told ABC News, taking issue with the methodology that the study used to translate harms from swallowing into harms from inhaling the chemical. But extrapolating data from oral toxicity studies to inhalation exposure is a common practice among regulatory agencies, according to the study’s authors.

“With pulegone known to be a potential human carcinogen, and in the background of youth epidemic and the recent hospitalizations of e-cigarette users, relying on the absence of respiratory data is irresponsible,” said Jabba.

Earlier this year, researchers from the University of California at Riverside published an extensive chemical analysis of JUUL liquids, which found detectable levels of pulegone in “Cool Mint” and “Classic Menthol” flavors.

“Pulegone is only present in JUUL e-liquids in very small quantities, as a naturally occurring constituent of mint flavoring,” said JUUL spokesperson Lindsay Andrews. “Based on the calculation in the study, in order to reach an exposure level above the threshold of carcinogenic concern for pulegone, a person would have to consume hundreds of pods per day.”

However, the specific concentrations of pulegone in JUUL products have not been published, and therefore the study’s authors could not calculate the potential harm independently.

“It is possible JUUL’s products have only small amounts of pulegone, alleviating concerns, or perhaps more,” Jordt said, but we cannot know in the absence of absolute concentrations of pulegone in the e-cigarette liquids. “It is fairly simple for flavor chemists to redesign flavor mixes omitting pulegone, using synthetic mint oils, so it is hard to understand why the industry is so sensitive about it,” Jordt told ABC News.

If mint and menthol are banned in these products, there are other menthol derivatives with cooling effects that may be used as substitutes, Jabba said, adding that these alternate additives haven’t been studied.

According to the FDA’s most recent announcement, all flavored e-cigarettes other than tobacco flavor are potentially on the chopping block.

But in New York, Governor Andrew Cuomo’s ban on flavored e-cigarettes enacted on Tuesday does not apply to menthol flavors. While mint flavors have been included in the ban, as they are considered sweeter and more appealing to youth, stores will still be able to sell menthol flavors.

“The menthol flavor for the vaping helps menthol cigarette smokers,” explained the Governor. He highlighted the “very limited pool” of smokers for whom all other cessation methods have failed.

But mint and menthol flavor usage, grouped together, has surged in popularity among high schoolers from 51% to 64% from 2018 to 2019. These were the only flavors that increased in popularity over the year.

“We’re still looking at menthol and very well may end up including it in the ban. It’s not totally in the clear just yet,” a spokesperson for the Governor’s office told ABC News.

Lauren Kelly, MD, MPH, is an Internal Medicine resident physician in New York City working with the ABC News Medical Unit.