Some points on what has been discussed:
- For some people, smoking suppresses asthma. When they stop smoking, whether they are vapers or not, the asthma comes back with a bang. This can confuse the issue mightily. It's a well-known effect because when you think about it, an asthma sufferer should be well and truly done in by smoking - but they're not.
- It is impossible for all liquids to be well-tolerated by all vapers. Ain't gonna happen. You have to test and trial, especially if you have a new breathing issue. Especially if you changed something recently. Flavourings are the big issue here, but not always the whole story.
- All PG is very similar as it is all synthetic. However the contaminant percentage content varies widely according to how much it costs, basically:
Industrial grade
Agricultural grade
Food grade
Pharmaceutical grade
Only pharma grade is suitable for inhalation, all other grades are guaranteed to contain contaminants in higher amounts. All it takes is for your e-liquid vendor to buy a cheap grade and there you go. Try another vendor with higher quality values.
- Although all PG mixes should essentially be the same, as PG is a synthetic product, the same is definitely not true of glycerines. They are made from so many different feedstocks, in so many different ways, that it can be guaranteed that someone will be intolerant to a variety that others find no problem to vape. The grade/cost issue is the same of course - you can't tell if they are using cheap rubbish or not, so try another brand. None of them post a full analysis of their finished retail product monthly, and there are good reasons for that. Cost of testing isn't really a factor for firms turning over hundreds of thousands of $$ a year (and certainly for those turning over millions a year, and there are many more of those than you think). There are other reasons, none of them valid in my mind. I just don't trust anyone who won't post an analysis, and that's all there is to it.
There are all sorts of issues with glycerine feedstock sources. Contamination, biodiesel byproduct glycerine getting into the chain, jatropha plant toxins getting in there, etc etc. Here's a story that might convince you:
I am a 100% glycerine vaper because at first I had issues with PG. That has receded now but I stick with glycerine because it works for me. I don't call it VG by the way because the finest quality of all now is synthetic glycerine like Dow's Optim, it is 100% synthetic and 100% pure, and also many pharma sources are changing their PG inhaler base over to that as they find it's a better choice. It's true that 3 years back, veg glycerine was the best choice as animal glycerine was the main alternative.
Anyway, I've tried lots of glycerines and most are OK for me. A while back, though, I got a new one to try. On day 2, I was having breathing issues. On day 3 breathing was becoming difficult. I stopped using that brand as it was obvious what the problem was. If I'd stayed with it, on day 4 I'd have been in hospital and in deep wotsit.
So there can be significant differences between glycerines. Yes Ecopure is safe, because it's expensive, because if they had any kind of user issue with it they would literally lose millions (it's complicated why, but they would).
I challenge anyone to show me something cheap and safe, and prove it with a 99.5% analysis by GC-MS and LC/LC and/or whatever else it takes to get to a 99.5% analysis including the water content. Strangely, you won't see many full tests on vendors' sites. None, at least for current analyses, as far as I know. Maybe because they are trying to sell you something 'cheap and safe'.
There ain't no such animal. Prove me wrong.