So I would say that the two key differentiating factors are actually the air content and the fat content rather than the source of the ingredients used for flavouring.
For e-cigarettes, using a liquid solution instead of dried tobacco has become popular; this e-liquid contains water, nicotine, a base and occasionally flavourings, and vaporizes at a much lower temperature.
Although the start-ups are confident they will get the green light, the technique is already used for flavourings and insulin, they worry about the time this will take and about labelling disputes.