In another thread there was a chemical analysis from a lab in Naples (written in Italian). It is very blurry, and it does not test vapor - only the chemicals in the filter (plus liquid, I assume, as the product is RY4), and the plastic casing. In the filter results, there is a section about carcinogenic chemicals (hydrocarbons), which amount to less than o.5 mcg, plus nicotine, which in this case was 3.38 mg.
The plastic filter casing contains quite a few metals (in micrograms-per-liter amounts), plus benzene, styrene, and others in trace amounts. I have no idea how much of this gets into us, and whether these quantities are dangerous.