US officials are working to track down a chemical contaminant that is potentially behind a rash of lung illnesses connected to vaping.

The Washington Post reported that while the investigation was ongoing, some state investigators had identified a potential lead: oil derived from vitamin E. Vitamin E can be found in almonds and avocados, and the oil is commonly used in beauty products and nutritional supplements. But inhaling it could pose risks. It acts like a grease coating a vaper’s lungs, Bryn Mawr College chemistry professor Michelle Francl told the Post.

Vitamin E acetate acts like a grease coating a vaper’s lungs

The Washington Post reported that officials conducting an investigation at the Food and Drug Administration found vitamin E acetate in cannabis products used by those with the illness. The substance was also present in almost all the cannabis products used by sick patients in New York where 34 people have come down with the severe lung illness.

Investigators were also looking into contaminants and bootleg vape products as potential culprits. On Thursday, New York State Health Commissioner Howard Zucker said in a statement that vitamin E acetate became “a key focus” because it isn’t an approved additive for medical marijuana vape samples and wasn’t present in the nicotine products health authorities tested. The statement said vitamin E acetate was present in “very high levels” in “nearly all cannabis-containing samples” tested by the state.

But the investigation is far from over, and there are many other potential culprits out there. The Centers for Disease Control and Prevention issued a press release on September 6th saying that it is looking into a broad range of chemical contaminants since infectious disease has been ruled out. It clarified that no one substance — including vitamin E acetate — had been found in all of the 120 samples it has collected, and they were sent to the FDA for testing.

“Importantly, identifying any compounds present in the samples will be one piece of the puzzle but won’t necessarily answer questions about causality, which makes our ongoing work critical,” acting FDA Commissioner Ned Sharpless said in the release.

According to the CDC, as of August 27th, there have been 215 cases reported across 25 states of the mysterious lung illness. Most of the patients are teens and people under 40, according to the CDC, which isn’t surprising since the US surgeon general called vaping an “epidemic among youth.” Their symptoms include shortness of breath, difficulty breathing, chest pain, vomiting, diarrhea, and fatigue. Two people have died so far after being hospitalized in Oregon and Illinois.

The CDC had warned vapers to avoid using e-cigarettes and related products that have been modified or bought off the street. It’s now saying that people should consider not vaping at all while the investigation is ongoing.

Update September 6th, 3:15PM ET: This post has been updated with information from the CDC.