The Mysterious Vaping Illness That’s ‘Becoming an Epidemic’ - The New York Times
... vaping has its own problems: Nicotine or THC, the high-inducing chemical in marijuana, is mixed with solvents that dissolve and deliver the drugs. The solvents, or oils, heat up during aerosolization to become vapor. But some oil droplets may be left over as the liquid cools back down, and inhaling those drops may cause breathing problems and lung inflammation.
“Inhaling oil into your lungs is extremely dangerous behavior that could result in death,” said Thomas Eissenberg, who studies vaping at Virginia Commonwealth University. “That is probably the biggest message we can get out of this.”