People who want to spread fear about vaping will be raising issues about individual flavorings in the coming months and years. Of course flavorings need to be researched much more extensively, and flavorings that represent true risks (at levels of concentration typical for vaping) must be controlled or even banned. The issue is not simple, as each flavoring is chemically unique, so there can be no general rule. Furthermore, some flavorings that are safe to eat can be dangerous when inhaled in significant quantities, for a significant period of time. Case in point, diacetyl.
Some journalists have recently noted the presence of diacetyl, the buttery-flavor additive, in some e-liquids with butterscotch or caramel flavors. Some of the articles on the subject do not mention concentration levels, or consumption volumes and time extents, at which the substance causes risk. This lapse is typical of medics, journalists, and politicos who oppose vaping, and it is a lapse so serious that it discredits their charges.
There are hundreds, probably thousands, of "dangerous" substances that regulators allow in foods and inhalants, because they are present at such low levels of concentration that they incur negligible risk. The list includes, just for instance, insect body parts and excrement, which are impossible to totally keep out of factory produced foodstuffs. But the list also includes a great variety of chemical substances which are harmless when present in "trace amounts". Many of the chemicals named by vaping opponents as dangerously present in e-liquid or vapor are in fact present only at trace levels, but this is seldom mentioned by those who raise the issues as an anti-vaping argument.
Anyone who publicizes a statement that an e-liquid or vapor component is toxic, WITHOUT MENTIONING LEVELS OF CONCENTRATION, is engaging in charlatanism, no matter how impressive his or her medical credentials, no matter how prestigious the publication. Anyone demanding that a potentially life-saving device must not be allowed until it is proven to be 100% safe is presenting a bogus scientific framework. NOTHING is 100% safe, not even the air you breathe. Indeed most especially not the air you breathe! Responsible regulatory science is about determining acceptable levels of risk and regulating substances so that they fall within those acceptable levels.
And so now to the case in point: diacetyl. It is the substance that makes "buttered" popcorn and margarine taste like butter. It is a natural substance, a by-product of fermentation. It is perfectly safe to eat, and approved for consumption (by mouth) by all the appropriate regulatory bodies. But it turns out that long-term inhalation of significant quantities can damage the lungs, a fact that was discovered when workers in popcorn factories started showing up in clinics with lung ailments.
These dangers have been known by the vaping industry and community for a number of years, but apparently some e-liquid manufacturers have not heeded warnings, and continue to use the substance. Of course it is not yet known what levels or time extents (duration of regular vaping of the substance) are dangerous, IN THE CONCENTRATIONS TYPICAL FOR VAPING. Perhaps diacetyl should be banned or restricted. Perhaps vapers will have to do without butterscotch. Or perhaps other, safer, butter-flavored additives can be found. Has anyone considered, like, uh... butter?
This, and other issues like it, are precisely why responsible research and regulation are necessary in order to make vaping fully safe. Vape-bashing and fear-mongering are not responsible research and regulation.