Wizard Labs is
very good about describing the ingredients in the flavorings they carry from the different manufacturers. They usually also include additional info
right from the manufacturer as well (always true with TFA flavorings especially). That way, you don't have to go from website to website for each manufacturers' info! Since I
buy mostly TFA flavorings...I look for details like the following, where WL denotes any presence of D, AP, or A with wording like this example below:
***Note: This flavoring contains trace amounts of the "custard note": Acetoin
I then just
buy the DX version of that particular flavoring, if there's one available. Sometimes there's even a different flavoring altogether...that will give your liquid a similar taste (ie. TFA Vanilla Custard has thing(s) you want to avoid, but Vanilla Swirl does a good job as a substitute and
doesn't have those things in it).
***I'm not saying that other companies besides WL
don't also do that though. I buy all my flavorings from them, so I'm just familiar with what
they include about flavorings. They're 50 miles from me, their packaging & care is superb, the prices & quality are great, and customer service is excellent. So I just stick with them. Plus, it's usually a quick turn-around when I order.