I did cough in the mornings when I smoked, and did get a fair bit of sinus congestion & pain.
Now I cough, but it's upper respiratory congestion based rather than a smokers 'lung cough'. The sinuses are much better, but I do get a bit of nasal and throat congestion with probably the VG.
When I read about the diacetyl etc., it did ring a few bells with me because early on, I found myself reacting badly to some brands of Custard & Vanilla. One seemed to literally shred my throat, and a few made my gums bleed, my throat swell or my breathing become difficult too.
Then, once I built up to getting problems with PG, the whole thing became even harder to define until I changed to all VG, then it was easy once more to recognise the flavours that caused me problems.
I also found myself getting breathing and throat problems with certain other flavours too: strawberry, blackberry & lime for instance. It was bad enough having to find my way around PG, but getting flavours that cause me problems too made it twice as hard. Never mind - almost 6 months so I've got his far. For someone who never had any allergies, it's been/is difficult at times.
I found the article on the TPA website about the subject very interesting and honest, plus I like that they took the time/effort to test their flavours and now give details about any such substances present in individual flavours. They also have some vanilla/cream/custard type flavourings that have been developed without them.
Now and then I do see vendors showing initiative and giving such information about their liquids now. Hopefully, this practice will become more commonplace once they realise that stating there is no Diacetyl used is not enough ...they need to understand that it's diacetyl, acetoin, & acetyl propionyl, and perhaps read something like the TPA article:
Perfumer's Apprentice
To me, the fact that it's known for these substances to have the
potential to cause lung problems means extreme caution needs to be exercised when manufacturing/using such things for vaping liquids. After all, it takes the inhalation issue a step further in that it's heated and taken directly into the body rather than being an airborne particulate.
No good it being assumed that it'll be OK and then finding it isn't years down the line. If it's suspect, replace it with something more benign.
Now that we're using more sophisticated equipment, with more powerful batteries, these issues may need even more attention to detail, and I suspect that in the case of the major flavourings manufacturers, the issue is being investigated and dealt with accordingly. At such a relatively early stage in the vaping practice, I'm sure there's much to be learned, tweaked and developed for the better good, and the better diligence applied to these issues, the less validity can be given to the naysayers and negative reports ...hopefully!.
Buying from UK suppliers that we can easily ask for such details is one step we can take right away.