(NBC NEWS) — The lung injuries linked to vaping may be caused by exposure to toxic chemical fumes.

That is according to a small study from the Mayo Clinic.

Researchers studied lung biopsies from 17 patients who were thought to suffer from vaping-related lung injuries.

They found no evidence of tissue damage caused by the accumulation of fatty substances such as mineral oils.

But they did find patterns of chemical injury which is often found after being exposed to toxic fumes and poisonous gases.

Experts say more research is needed.

So far, at least 17 people have died from vaping-related lung injuries and the CDC has reported more than 800 cases.