The safety of e-cigarettes has been an ongoing topic for a while.

Research has shown how e-cigarettes can be bad for your health in various ways.

But a new study suggests that the flavourings used in e-cigarettes might potentially be the most toxic part of the vapour inhaled by users.

What makes the flavour so dangerous?

E-cigarette liquid contains dozens of different chemicals, and these vary widely from product to product, said lead author Flori Sassano. She is a research project manager with the University of North Carolina School of Medicine.

Many of these chemicals are toxic to human cells in the laboratory, but the most toxic appear to be those related to the flavourings contained in e-liquids, Sassano said.

These chemicals include vanillin and cinnamaldehyde, which respectively produce the flavours of vanilla and cinnamon.

The flavourings have been approved by the US Food and Drug Administration (FDA) for consumption, but that doesn’t mean they are safe to inhale as vapour from an e-cigarette, Sassano explained.

The FDA’s list of safe flavourings “is based upon studies that have been done on these chemicals when ingested, but not when inhaled,” she said.

Not all flavours tested

There are more than 7 700 e-liquid flavours on the market from more than 1 200 different vendors, and most have not been tested for their potential toxicity, the study authors said in background notes.

For their research, Sassano and her colleagues tested about 150 commercially available e-liquids, and out of those identified 143 unique chemical compounds.

“What this tells us is these e-liquids are very diverse, and because they are diverse they are very hard to study as a group,” Sassano said.

What the study entailed

To test toxicity, the researchers developed a system by which lab-grown human cells are exposed to e-liquid chemicals. The more toxic a chemical, the more it will reduce the growth rates of these cells, according to the report.

Most of the liquid in an e-cigarette is made up of propylene glycol and vegetable glycerine, and those chemicals on their own are toxic to lab-grown human cells, the researchers said.

But the flavourings added to e-cigarettes can be even more toxic, the investigators discovered.

The toxic effects of these liquids proved harmful to cells from human lungs and upper airways. And, overall, the more ingredients included in an e-liquid, the greater the toxicity, the findings showed.

The study was published online in the journal PLOS Biology.

Sassano said the process they’ve developed provides a fast and reliable way to evaluate the toxicity of the chemicals in e-liquids.

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