Five months after the outbreak of a mysterious e-cigarette lung disease, researchers at the Centers for Disease Control (CDC) say they have pinpointed the cause as vitamin E acetate, an ingredient often added to cannabis vape products.

While CDC director Dr. Anne Schuchat said in a press briefing that the discovery is “significant” and a “breakthrough,” she says further study is necessary. She also cautioned that other ingredients may be responsible and that the disease, dubbed “E-Cigarette VAping Lung Injury” (EVALI), may have multiple causes.

What is Vitamin E Acetate?

Also known as tocopheryl acetate, the substance now believed to be that cause of e-cigarette lung disease is an ester, or chemical compound derived from acetic acid, a component of vinegar. When combined with tocopherol (vitamin E), is frequently taken as a nutritional supplement and used in the manufacture of cosmetics.

It is also “enormously sticky” when it enters the lungs, according to one physician working at the CDC. It leaves a coating on the surfaces of the air sacs (alveoli), which can interfere with lung function.

Suspicions about vitamin E acetate were raised in September when scientists at the Wadsworth Center in New York discovered the substance in samples of cannabis vape liquids. At that time, the FDA confirmed that approximately 56 percent of vape liquid samples that had been submitted by state health authorities across the country tested positive for vitamin E acetate.

Why Vitamin E Acetate?

This substance appears to have been added to home-made or bootleg marijuana vape oil as a thickening agent. Most victims report having obtained their cannabis-based vape products from “informal sources,” i.e., street dealers, friends or family, or unlicensed online retailers marketing counterfeit or “bootleg” vape oil. It does not appear to have affected commercial cannabis vape from licensed stores in states that have legalized recreational marijuana, nor in nicotine-based vape manufactured by companies such as Juul Labs.

In interviews with 86 people in Illinois and Wisconsin who got ill after vaping, CDC researchers found that 57 of them had used products from a company calling itself “Dank Vapes.” The brand appears to be nothing more than a label used by the underground, bootleg marijuana industry, designed to make home-brewed products look legit. These ingredients have never been safety tested.

Nonetheless, because the nature of the new e-cigarette lung disease is not fully understood, the CDC is strongly recommending that people cease using all vape products until more is known.

What Else Might be Causing E-Cigarette Lung Disease?

Because there are so many ingredients in both nicotine and cannabis vape, scientists have been hesitant to point to any single cause of EVALI.

Some of the agents used to create candy and fruit-flavored vape oils have been under scrutiny. These flavoring agents by themselves and at room temperature are fairly innocuous. However, when heated, they undergo chemical reactions that can cause them to become toxic.

In fact, health care providers have noted that in a number of EVALI cases, patient injuries were strikingly similar to chemical burns.