Toxins produced by e-cigarettes vary by flavour

The researchers analysed popular e-cigarette flavours and the amount of free radicals they produced and found that many of the chemicals used to flavour e-cigarettes increased the production of free radicals, while a few actually lowered it.

John Richie, professor of public health sciences and pharmacology, Penn State College of Medicine, says the results are an important step in learning more about the potential dangers of e-cigarettes.

"When these products first came on the market, many people were saying they were harmless and that it was just water vapour," Richie said. "We know that's not true, but we also don't have the numbers on how dangerous e-cigarettes are. But now we know that e-cigarettes do produce free radicals, and the amount is affected by the flavourants added."

Free radicals are unstable molecules that can cause damage to healthy cells, and have been linked to conditions like inflammation, heart disease and cancer. Consumers inhale these free radicals when they smoke a combustible cigarette.

While e-cigarettes do not give off smoke, they do contain many different chemicals to flavour the e-liquids, which are absent from traditional, or "combustible," cigarettes. The researchers say that while the flavourings are approved for consumption, they aren't evaluated for safety when heated.

"E-cigarettes have a coil for heating the liquid that gets quite hot and may aid the production of free radicals," Richie says. "It's important to look at the effect of flavours on these free radical levels because e-cigarettes come in hundreds of flavours, many of which are marketed toward kids, like bubblegum."

The researchers measured the free radicals produced by 50 flavours of a popular brand of e-cigarette and compared them to flavourless e-liquid. They found that about 43 per cent of the flavours were associated with significantly higher levels of free radical production, while a few were associated with lower levels.

Next, the researchers broke down the flavours into their individual chemicals to see which ones were associated with higher levels of free radicals. Zachary Bitzer, post-doctoral scholar, says isolating the chemicals was important because flavours are not consistent across brands.

"Two different manufacturers may sell an 'orange' flavoured e-liquid, but they could each contain vastly different flavourants to get that orange flavour," Bitzer says. "Just like Coke and Pepsi are both colas but have different ingredients, different flavours of e-cigarettes may contain different flavourants, resulting in different levels of free radicals."

The researchers found six flavourants that significantly increased the production of free radicals. These flavourants included linalool, dipentene and citral, which are often used to give products citrus or floral notes. Additionally, the flavourant ethyl vanillin — often used for vanilla notes — decreased the production of free radicals by 42 per cent.

Richie said the results — recently published in Free Radical Biology and Medicine — could help consumers make better decisions about the products they buy, as well as help policy makers create regulations around e-cigarettes in the future.

"We found that many of these flavourings increase free radicals, but a few decreased them, as well, which raises the possibility that maybe there are things you can add to these liquids that could reduce radical production and might make them safer," Richie says. 

"E-cigarettes are regulated by the Center for Tobacco Products in the FDA, and I think these results can be useful to help set guidelines in terms of regulating these products," he adds.