Authorities are zeroing in on an additive in some THC and other vaping products as a “potential toxin” that may be cause of thousands of mysterious vaping-related illnesses, officials with the Centers for Disease Control and Prevention (CDC) said Friday.

The potential breakthrough is centered on a Vitamin E acetate, which was found from in lung patient samples from sick patients. The acetate was found in all 29 samples that were collected and tested, Dr. Anne Schuchat, the CDC’s principal deputy director, said during a teleconference with reporters.

THC, the main psychoactive ingredient in cannabis, was found in 23

Read more: US: CDC makes breakthrough in mysterious lung illnesses