Trace amounts have been found in some e-liquids, some much worse than others. We have never heard of any reports of popcorn lung due to vaping. The only known reports were over a decade ago with popcorn factory workers exposed to raw Diacetyl powder when pouring it into boiling butter vats for mixing. Cigarettes have been shown to contain up to 700 times more diacetyl than e-liquids containing the most diacetyl that were tested, to date no smokers have ever been diagnosed with this condition. If diacetyl is a concern, avoid buttery, dessert flavours such as cheesecakes and custards but can still be found in even some fruit flavours.