A toxic chemical has been found in the lungs of 17 people afflicted with vaping-related illnesses — providing vital clues into the nationwide e-cigarette health crisis.

The Mayo Clinic in Arizona tested 17 lung biopsies from patients and victims around the country and found their injuries were likely caused by “direct toxicity or tissue damage from noxious chemical fumes,” ABC 15 Arizona reported Wednesday.

“It seems to be some kind of direct chemical injury, similar to what one might see with exposures to toxic chemical fumes, poisonous gases and toxic agents,” said Dr. Brandon Larsen, a surgical pathologist at Mayo Clinic Arizona.

The report came as authorities announced that an Alabama man had become the 17th person to die in the epidemic — while more than 800 have become sick.

Experts have been desperately searching for answers, suggesting the mysterious deaths were caused by heavy metals or an accumulation of fatty lipid acids in the lungs.

But Larsen said the Mayo Clinic believes the cause is “toxic byproducts” within vape liquids.

“Everyone should recognize that vaping is not without potential risks, including life-threatening risks, and I think our research supports that,” Larsen said, calling for immediate regulation of the industry.