For the first time since the outbreak of lung illnesses associated with e-cigarettes earlier this year, the Centers for Disease Control says it has identified a specific ingredient as a "very strong culprit": Vitamin E acetate.

Also known as tocopheryl acetate, Vitamin E acetate is a colorless, odorless additive sometimes found in skin-care products that makers of black-market marijuana vape pods have been using as a thickening agent for THC oils — or to dilute THC oils to make them more profitable. As the New York Times reports, the CDC says the finding is based on samples taken from the lungs of 29 of those sickened from vape use.

At a news briefing Friday, Dr. Anne Schuchat, principal deputy director of the C.D.C., said that the lung samples "provided evidence of vitamin E acetate at the primary site of injury in the lungs."

Health investigators have pointed to Vitamin E acetate as a potential culprit in the illnesses since early on in the outbreak, and health officials in New York earlier reported their suspicion of the ingredient in September.

More than 2,000 people have been made ill from vaping in the last seven months, and questions have consistently arisen about whether a particular ingredient might be to blame — or whether the process of inhaling any type of vapor through an e-cigarette might be dangerous in itself.

As NBC News reported earlier, many of the lung illnesses have been diagnosed as lipoid pneumonia, in which large amount of lipids, potentially from inhaling vaporized oil, become concentrated in the lungs.

Vitamin E acetate is not found in Juul products, for instance, though it's not yet clear what products besides those bought on the black market might have been using the additive, believing it to be harmless.

Most of the patients who have fallen ill or died from vaping had used THC in some form — though as the Washington Post notes, in at least three cases, THC was found in the systems of patients who said they had not vaped or consumed any pot.

If you're interested, you can read the CDC's weekly Morbidity and Mortality report here.

Previously: CDC Issues Broad Warning About Vaping, and SF-Based Juul Is Not Having the Greatest Summer