U.S. health officials say they have found the likely cause of a mysterious illness in people who smoke e-cigarettes, describing the findings as a "breakthrough."
Anne Schuchat of the Centers for Disease Control and Prevention said Friday that a compound known as vitamin E acetate is a "very strong culprit" in the search for the cause of the mysterious lung disease.
Schuchat, who is the CDC's principal deputy director, said the compound was found in fluid samples taken from the lungs of 29 patients across the country who were diagnosed with the vaping illness.
"We are in a better place in terms of having one very strong culprit," she said.
Schuchat cautioned that more work needs to be done to confirm that vitamin E acetate causes lung damage when inhaled, and said there could still be other toxic substances in e-cigarettes that lead to lung disease.
More than 2,000 Americans who smoke e-cigarettes have gotten sick since March, and at least 40 of them have died.
Health officials say that vitamin E is safe as a vitamin pill or to use on the skin, but that inhaling it can be harmful.
The compound is sometimes used as a thickener in vaping fluid, especially in black market vape cartridges and those containing THC - the component of marijuana that gets people high.
E-cigarettes have been available in the United States for more than a decade. They work, in general, by using a battery to heat a liquid nicotine solution and turn it into an inhalable vapor.
While e-cigarettes contain nicotine, which is addictive, they have been considered safer than traditional cigarettes because they do not contain tar or many of the other substances in traditional cigarettes that make them deadly.
Advocates of e-cigarettes say they are a powerful tool to help adult smokers quit smoking traditional cigarettes.
However, critics say that e-cigarettes are making a new generation addicted to nicotine. They also point out that the long-term health consequences of vaping are not known, and say that e-cigarettes could contain other potentially harmful substances, including chemicals used for flavoring and traces of metals.