Anne Schuchet, CDC principal deputy director, said in a telephone briefing on Friday its research was "significant, because for the first time, we have detected a potential toxin of concern".
The organization said that recent CDC laboratory testing of bronchoalveolar lavage (BAL) fluid samples from 29 patients with EVALI submitted to CDC from 10 states found vitamin E acetate in all of the BAL fluid samples.
The agency said it identified 29 cases of vaping-related illness connected to vitamin E acetate found in biological samples from patients.
This outbreak has been of special concern for those living with HIV or other chronic illnesses since many have switched to vaping nicotine products because it appears healthier than smoking cigarettes.
The CDC has not changed its warning against using these illegitimate products and continues to urge Americans who don't use e-cigarettes not to start.
She has not ruled out other chemicals as possible causes for the illness.
"No single product or substance has been linked to these injuries although most cases reported vaping THC", MDHHS said. "Adults who choose to continue using vapor products have the freedom to choose tobacco flavored vapor products from licensed retailers, as tobacco flavored vapor products remain on the market legally".
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Vitamin E acetate is a common additive in many cosmetic and food products; it is considered safe when applied to the skin or consumed, but evidence indicates that it may be unsafe when inhaled. Half of those THC-containing products also had vitamin E acetate, with concentrations as high as 88%, the FDA said Friday.
It's not clear how vitamin E acetate might actually harm the lungs.
The discovery of Vitamin E acetate in lung samples offers the first direct evidence of a link with the substance and vaping-related lung injuries. Vitamin E acetate is sometimes added to dilute the THC to increase profits or as a thickening agent.
Hundreds of state and federal health investigators have been deployed to find out what has caused such extensive damage to patients' lungs, which researchers have likened to the chemical burns suffered by soldiers attacked with mustard gas in World War I.
Juul Labs, maker of the top-selling brand of e-cigarette, issued a statement after the CDC announcement, noting that its nicotine products do not contain THC or any vitamin E compounds.
Other potentially risky chemicals have been identified in vape products when heated and aerosolized, including many that even the creators might not have predicted.
Schuchet said that data shows that THC products bought from "informal sources" instead of licensed dispensaries "point to a much greater risk". "And so when it goes into the lung, it does hang around".