The Centers for Disease Control said Friday morning that vitamin E acetate is a “potential chemical of concern” in biological samples taken related to their ongoing investigation into vaping-related illness reported across the country.

The CDC conducted research concerning bronchoalveolar lavage from 29 patients with EVALI, the term the CDC coined to describe e-cigarette or vaping-related lung injuries. As of Tuesday, the CDC said it has received over 2,000 cases of vaping-related injuries and 39 deaths that can be attributed to the injuries. 

Vitamin E acetate was present in all 29 samples. The CDC said that the chemical is an additive in e-cigarettes and vaping products and that many with vaping-related illnesses have reported using THC vaping products. 

Despite identifying vitamin E acetate in the samples, the CDC noted that “no one compound or ingredient has emerged as the cause of these illnesses to date” and that there may be additional causes. 

“We are in a better place than we were a few weeks ago in terms of finding a culprit,” CDC Principal Deputy Director Dr. Anne Schuchat told CNBC. The agency reported that “many different substances and product sources are still under investigation.”

CDC officials said that additional studies are needed before confirming the relationship between vitamin E acetate and vaping-related illnesses, according to CNBC. 

“CDC recommends that you do not use e-cigarette, or vaping products, that contain THC,” their official release stated. Because no single compound has been definitively proven to be the culprit, “the only way to assure you are not at risk while the investigation continues is to consider refraining from use of all e-cigarette, or vaping, products.”