The human body, which is very complicated and still not fully understood bit of machinery (least of all by some doctors), has very poor quality control,
and the manufacturing variation between these different units is very high. (Would not even be acceptable to Fastec)
So it is not surprising that the ingress of any outside chemical concoction (eg. vapour) could cause problems for some units.
In that respect vaping is similar to eating, in that ingress of some elements can cause undesirable attributes being developed by some units.
With regard to the human body and the use of the electronic/electric personal vaporizers (E-Cig) some units appear to have an adverse reaction to the chemicals contained within the nicotine delivery mixture (E-Juice).
This is usually due to a degree of intolerance to monopropylene glycol (PG) and a reduction or elimination of that chemical usually achieves fully functional status back to the units affected.
However some units have an intolerance to vegetable glycerine (although this is unusual) but again a reduction of that chemical from the mixture is usually sufficient in bringing the units affected back to full operational status.
The addition of flavourings to the E-Liquid brings further complications to the study, as just as in the intake of food, there is a wide perceived variation of acceptable flavours acceptable to individual units and it is difficult to determine, if any, adverse effects are physical or physiological.
Fortunately the author is not aware of any Marmite flavours on the market at the time of writing so the detrimental effects should be insignificant.
