MrNate: in theory you are correct, that cracking plastic is not necessarily an indicator of lung damage, it could just be thermal effects. And I do appreciate the rigor of trying to separate and understand the effects. But it is known that cinnamaldehyde is dangerous to the lungs. Don't have the links at my disposal now, but it is known. And there is a big difference to me between leaching plasticisers, which leads to cracking of plastic and makes you vape plasticisers too, and etching plastic, which is a breakdown of the polymer itself. Plus the lungs have their own surfactant, and inhaling others, like citrus oils, can disrupt that important barrier, if not dissolve lipid bilayers, as in cells. Lots of bio stuff dissolves in them, as well as some polymer compounds, as Katya said.
But, hey, for some these flavors are just too important, and thus vaping them, regardless of risk, is rationalized to be imperative. They are all legal, and people can vape whatever they want. Yes, I am a PhD chemist with 30 years of advanced training in physical, organic, biophysics, bio-inorganic, and theoretical research and teaching. I personally will not vape these oils, for the many reasons I and Katya have stated, based on my knowledge of them chemically, and the tissues they interact with. I don't think any of these are implicated in irreversible lung damage, like that caused by diacetyl, but there could be incremental and sustained lung impairment, which I thought was what we were trying to avoid by vaping.
Flavors are the Achilles heal of vaping, in my opinion. There are many wacky flavors out there that use compounds which are fine for foods, like meat flavors, but use compounds like organic acids, aldehydes and long-chain esters which really have been shown to be a significant risk to lung tissue, similar to diacetyl.
