Terry made me go look for it-diacetyl
Quoted from another thread...
"Originally Posted by cosmopaladin
You might know this already, but just in case you don't (you said you were new to vaping). From wherever you order check that they guaranty all of their flavors are diacetyl free. Diacetyl is used for a buttery/popcorn flavors and when vaporized at high temps and inhaled it, it can cause popcorn lung/Bronchiolitis obliterans which is not curable without a lung transplant. Anyways I know it use to be in some buttery flavored e-juice and should not be in any anymore. Any reputable places juices is likely ok. Just it is good to check or stay away from buttery flavors if you are really concerned.
Also if you do do DIY juices as someone else suggested, Lorann flavors, which most people use as flavoring is Diacetyl free or so the site sight says. Lots of people use it and I have yet to hear of any issues.
Good luck with finding a flavor you like."
I was close.