When you eat something, it goes into your stomach and mixed with gastric juices, then goes into your intestines where the broken down food is passed into your blood system. It is then filtered by your liver.
With inhalation, the chemicals go into your lungs and pass through to your blood system and are pumped to your brain. Inhalation is the quickest way to get any substance to your brain. This blood is not filtered by the liver and your lungs are more delicate tissue than your stomach.
The Flavoring and Extract Manufacturing Assn. (FEMA) is the agency which issues the GRAS designation. This is from their website:
- E-cigarette and flavor manufacturers and marketers should not represent or suggest that the flavor ingredients used in e-cigarettes are safe because they have FEMA GRASTM status for use in food because such statements are false and misleading.
- E-cigarette manufacturers and marketers should take appropriate action to assure the safety of flavor ingredients used in e-cigarettes. FEMA GRASTM status for the use of flavor ingredients in food does not mean that FEMA GRASTM flavor ingredients are safe for use in e-cigarettes.
The concern about vaping is clouded by the history of the tobacco companies. The tobacco companies used to say that while the individual components of their product might be harmful, they were in such small amounts that it didn't matter. "The dose makes the poison" as Paracelus said.
In the BBC documentary, "Death in the West", one of the scientists for Phillip Morris stated that anything can kill you if you get enough of it, even applesauce. The interviewer said that he didn't think applesauce was killing very many people. The scientist replied, "They're not eating enough."
A disease profile will likely emerge from long term vaping, but it will take decades before we see what the cumulative effect may be and if it is only some flavors that cause a detrimental effect.
It may be that vaping just becomes another vice like drinking. Many people drink responsibly and have no ill effects, however others are addicted which can compromise their health.