E-cigarette vapor isn’t smoke. There is no current evidence that inhaling a mixture of propylene glycol and vegetable glycerine causes any kind of long-term damage. However, there may be risks in inhaling some flavorings. There are flavoring agents found in some e-liquid that have been linked to a condition known as bronchiolitis obliterans, or popcorn lung. These chemicals — diacetyl and acetyl propionyl — are probably responsible for cases of popcorn lung at some flavoring factories, where workers inhaled large quantities of the substances in powdered form.
