In what may be the biggest health scare to hit the cannabis community since the wave of legalization in recent years, people are freaked over the lung illness which has struck some vape pen users across the country.

Dozens have been hospitalized and three deaths are suspected in connection with “chemical pneumonia” from poisonous irritants in cannabis and nicotine vape cartridges. But what exactly that poison is has remained mysterious since the outbreak began.

However, things have started become a little less mysterious in recent days. On Thursday New York State’s Department of Health announced that they had found the possible culprit, a thickening agent called vitamin E acetate.

Health officials said there were “very high levels” found in some of the cartridges related to poisoning cases, as reported by the New York Times.

An article from Leafly mirrors the findings of New York State, and also points to why the lung disease emerged so suddenly this year. The website reported on a diluent called Honey Cut, which was introduced to the vape cart market in late 2018. One source told Leafly that Honey Cut had tested positive for Vitamin E oil.

Honey Cut is attractive to sellers because it can dilute THC oil without actually making it thinner. The product was only available through an anonymously-run website, which went dark after Leafly’s report. Similar products have also been pulled from online distributors in recent weeks.

While some signs are pointing to Vitamin E additive as the source of the outbreak, the Times notes that the discovery “by no means ends the search for what is causing the illnesses, particularly given that vitamin E acetate has not been confirmed as a factor in the majority of cases in which patients have gotten sick in New York.”

So far, the brand names associated with the respiratory illness includes Chronic Carts, Dank Vapes, and West Coast Carts. Health officials recommend that users stick to lab-tested vape cartridges sold from licensed pot shops or, if they really want to 100% safe, go with flowers for the time being.