There's now solid evidence that vitamin E oil found in bootleg THC vape products is behind at least some of the 2,000-plus severe vaping-related lung injuries nationwide — a finding the Centers for Disease Control and Prevention calls a "breakthrough" in the investigation.

"For the first time, we have detected a potential toxin of concern: vitamin E acetate," Dr. Anne Schuchat, CDC's principal deputy director, said in a call with reporters on Friday. Vitamin E acetate, an oil, is a synthetic form of vitamin E.

Investigators tested samples of fluid taken from the lungs of 29 patients with vaping illness in 10 different states, and found vitamin E acetate in all 29. No other oils, such as mineral oil or plant oils, were found at high levels.

"These findings provide direct evidence of vitamin E acetate at the primary site of injury within the lung," said Schuchat, adding the oil had previously been detected in product samples. In September, the New York State Department of Health said that lab tests showed extremely high levels of vitamin E acetate in nearly all of the analyzed samples of products that contained cannabis.

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Vitamin E is found in many common products, from food to supplements to skin care lotions, and there is no evidence it causes harm when swallowed or applied to the skin.

When inhaled, however, it appears to cause problems. One official described inhaled vitamin E acetate as a coating of honey that sticks around in the lungs.

Still, investigators say they cannot yet rule out other possible toxins or ingredients that may be causing the illnesses. There may be multiple causes, and the CDC says it will continue to test vaping aerosols.

Nearly all of the 29 patients in the CDC analysis also reported vaping THC, the marijuana ingredient that gives users a high.

In a separate report also published by the CDC Friday, health officials with the Illinois Department of Public Health reported the majority of their patients said they'd used pre-filled THC vape cartridges that they had gotten from friends, off the street or other informal sources.

They compared data from patients with the lung illnesses with survey responses from more than 4,000 people who said they vaped but never became ill.

The overwhelming majority of healthy people who reported vaping — 94 percent — said they vaped nicotine only.

Patients who were ill were much more likely to report vaping THC products. What's more, they were "roughly nine times more likely to obtain the THC-containing products from informal sources, such as a dealer, off the street or from a friend, compared to survey respondents," Dr. Jennifer Layden, Illinois' chief medical officer, said during the call with journalists.

Vaping-illness patients were also eight times more likely to say they'd used Dank Vapes, a known counterfeit product.

On Thursday, the CDC confirmed 2,051 cases of the vaping-related lung illnesses and 39 deaths.

The Trump administration is poised to take some kind of action on vaping. Earlier Friday, the president told reporters outside the White House that his team is “close to a final report” on the matter, saying it would be revealed next week.

“We have to take care of our kids most importantly. We’re going to have an age limit of 21,” Trump said, presumably referring to raising the national age to purchase tobacco products to 21.

In September, the administration announced it would ban e-cigarette flavors, including mint and menthol, though that has not been formalized. The president’s comments Friday appeared to leave room for a compromise that would benefit companies or vape shops that sell the products. “We’re also talking about keeping people working,” Trump said.

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