Authorities at the US Centres for Disease Control and Prevention (CDC) are finally zeroing in on one of the substances in vapes that could be making people sick.

"For the first time we have detected a potential toxin of concern: vitamin E acetate," CDC principal deputy director Anne Schuchat said on a call with reporters Friday.

The CDC has taken a look at lung samples taken from 29 patients across 10 different US states and found vitamin E acetate in all of them.

"Vitamin E acetate is enormously sticky," Jim Pirkle, from the CDC's environmental health lab, said on the call.

"You can think of it to be just like honey. And so when it goes into the lung, it does hang around."

Vitamin E acetate was previously identified as a concern in New York state, when high levels of the substance turned up in "nearly all cannabis-containing samples analysed" in September, according to a state health department release.

FDA commissioner Ned Sharpless also voiced his concerned about vitamin E acetate in a September tweet, saying it was "found in many of the samples containing THC."

The CDC said that vitamin E acetate is often found in illicit street-bought vapes. It's used to dilute liquid in vapes, especially to water down THC. Investigators still aren't positive that vitamin E is causing harm, but there's definitely a link between more vitamin E vapes and more injuries.

"Vitamin E acetate usually does not cause harm when swallowed as a vitamin supplement or applied topically to the skin," Schuchat said. "However, previous non-CDC research suggests that when vitamin E acetate is inhaled, it may interfere with normal lung function."

Federal health investigators aren't ready to say that THC-free nicotine vapes are safe, though. They caution that there can be small amounts of vitamin E in any vape, and that there could be other dangerous substances lingering in the vapes which haven't been identified yet.

A small study of 31 healthy adults released by the University of Pennsylvania in August suggested, similarly, that some "harmless" oils like propylene glycol and vegetable glycerin (PG-VG) might undergo dangerous transformations as they heat up and aerosolize inside vape pens, potentially turning them into toxic substances.

Because the vaping industry is largely unregulated, there are hundreds of different chemicals in vape liquids on the market, making it impossible for people to know whether the ones they're using are safe.

The CDC is recommending that as the investigation continues, people should consider not vaping at all, but those who do should refrain from vaping THC, especially from "informal sources like friends or family, online dealers, or the illicit market."

"Until the relationship between vitamin E acetate and lung health is better characterised, it's important that vitamin E acetate not be added to e-cigarette or vaping products," Schuchat said. "Caution should be used before substituting other cutting agents or additives for vitamin E acetate."

At least 2,051 people have gotten sick across the US in recent months, and 39 have died after vaping.

This article was originally published by Business Insider.

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