Vitamin E acetate, an additive sometimes used in THC and other vaping products, may be to blame for a national outbreak of e-cigarette-related lung injuries that's linked to dozens of deaths, according to US Centers for Disease Control and Prevention officials.

Dr. Anne Schuchat, the principal deputy director of the CDC, said she would characterize it as a breakthrough in the agency's investigation, although more tests are necessary.

In the video above: US officials: ‘strong culprit’ in vaping illnesses

"These new findings are significant," Schuchat said during a press briefing on Friday. "We have a strong culprit."

There is still more work to do and the CDC said it is continuing to test for a wide range of chemicals.

In the video below: CDC reports 'breakthrough' in vaping lung injury probe

Your cookie settings are preventing this third party content from displaying. If you’d like to view this content, please adjust your Cookie Settings . To find out more about how we use cookies, please see our Cookie Guide.

"This does not rule out other possible ingredients," Schuchat said. "There may be more than one cause."

The CDC says its tests found vitamin E acetate in samples taken from 29 patients who were sick with vaping-related illness in 10 states. THC, or tetrahydrocannabinol, the primary psychoactive component of the cannabis plant, or its metabolites were detected in 23 of 28 patients. Nicotine metabolites were detected in 16 of 26 patient specimens.

More on 7NEWS.com.au

During the press briefing, CDC's Dr. James Pirkle described vitamin E acetate as "enormously sticky" when it goes into the lungs, and it "does hang around." Pirkle said it wouldn't be unusual for THC to be absent from some of the samples because it leaves the lungs faster. He added finding THC in 82% of the samples from 28 patients was "noteworthy."

The investigation

In September, New York health officials linked cases of severe lung illness to vitamin E acetate in cannabis-containing vaping products. At the time, investigators said it was "a key focus" of the state's investigation into the illnesses.

"The CDC's reporting supports what New York State's Wadsworth Center Lab has found in vape products tested since early September and reinforces the importance of the role that Vitamin E acetate may play in the current outbreak of vaping related illnesses," New York Gov. Andrew Cuomo said in a statement on Friday. "While no definitive cause has been found, as I've said from the very beginning: if you don't know what you are smoking, don't smoke it."

New warning

Until the investigation is complete, the CDC suggests people refrain from using all vaping products with THC, no matter where people buy them. The investigation has found that many of these products patients used were bought online or received through friends or family, rather than through vaping shops or at licensed THC dispensaries.

Vitamin E is used in several products, such as lotions and in supplements, but the CDC said there is a "big difference" in putting vitamin E on the skin or swallowing it in pill and in inhaling the oily vitamin.

Chevron Right Icon 'There is a big difference in putting vitamin E on the skin and inhaling the oily vitamin

Dr. Jennifer Layden, the chief medical officer and state epidemiologist with the Illinois Department of Public Health, said in the press briefing that in her state, they found the majority of cases of the people who were sick used THC, and that their materials came from "informal sources." In Illinois, she said, they had not had any cases associated with the state's medical marijuana program.

So far, there have been 2,051 cases of vaping associated illnesses, reported in every state, except for Alaska, as of November 5.

States have reported at least 40 deaths.