The Mayo Clinic released a report last week that characterizes the lung damage caused by vaping-related pulmonary illnesses as something more akin to chemical burns than anything else—something along the lines how a factory worker might be affected by “an industrial accident,” according to the New York Times. 

This means that the toxic fumes of vaporized oil may be the more specific culprit—rather than the oil itself or the thinning agents contained within (like vitamin E acetate). Much of the discussion thus far has centered around lipoid pneumonia, a condition caused when fat particles enter the lungs.

The Mayo Clinic report is the latest development in how vape manufacturers and retailers are coming to understand the mysterious disease that’s claimed 16 lives and racked up more than 1,000 reported medical cases, according to the Centers for Disease Control and Prevention (CDC). The nonprofit medical center published its findings in The New England Journal of Medicine, insisting that much remains unknown about this rash of illnesses. 

“Although the pathogenesis and the chemical agent(s) responsible for this problem remain unknown, this constellation of histologic changes suggests the possibility of direct lung toxicity from an inhaled noxious agent or agents,” the authors wrote.

Those chemicals, which end up “burning” or “torching” a user’s lungs, demand more scrutiny, according to the report. The precise effects aren’t clear yet, but the swelling caused by that chemical inhalation can shut down airways and interfere with normal breathing patterns.

“Based on the severity of injury we see, at least in some of these cases, I wouldn’t be surprised if we wind up with people down the road having chronic respiratory problems from this,” Brandon T. Larsen, a surgical pathologist at the Mayo Clinic in Scottsdale, Ariz., told the Times. “Some seem to recover. I don’t think we know what the long-term consequences will be.”

As the CDC has pointed out, the apparent source of much of the reported cases lies in the illicit market—fake brands of vape cartridges, like Dank Vapes, Moon Rocks and TKO, spreading across the otherwise fragmented cannabis market in the U.S. As legalization has slowly rolled out, the illicit market has grown more sophisticated in answering consumer demand for products like certain cannabis concentrates.

In response, governors in Massachusetts, Washington and Oregon have pushed back and called for bans on all vape sales—including those products sold in licensed dispensaries. (Washington’s ban hasn’t yet been approved, but Massachusetts implemented a four-month ban and Oregon implemented a six-month ban.) Critics say such responses will only push consumers back into the illicit market, where the problem began in the first place.