Well, on the flip side, I can honestly say (thru experience) that since I've started adding acids to my mixes, I have LESS congestion in my throat
I was just thinking about this. When I first started vaping (=smoking less) a hanging-on cough from a cold I had had got much worse for the first few weeks. Then it just disappeared, but I still had some amount of congestion. Then that also disappeared one-two weeks ago - about when I started adding vinegar.
Now it is back, and almost to the cough-level again, and it was starting to irritate me a bit. And I just realised that I haven't really been vaping much vinegar-added juice for the last few days (I don't add vinegar when I mix from Hangsen concentrates; the mouthfeel there is just perfect as it is)...
But thinking a bit further: it probably isn't the absence of vinegar in my vape that is causing the congestion and mild coughing. A much better candidate is extremely dry inside air, combined with the drying effects of vaping, combined with the slow process as my lungs are getting way less of tar etc than they've been used to for the last 26+ years.
Maybe I'm spoiled, since my juices are all VG, with small amounts of flavoring, so my normal vape is very smooth. The Malic acid I got at ecigexpress.com. The Lotioncrafter PG it's dissolved in (1.5 g/10ml) has aways been as OK as PG gets, and it's a very small amount anyway. The atomizer is a clean 1.8 ohm IKV i06 I use for testing liquids on a ProVari at 3.7 - 4.0 volts. For whatever reason, even at 1 drop per 3 ml, I find it causes that delayed slight dry cough. So I'll try acetic acid next, seeing as it's a liquid to begin with, if you follow my reasoning.
Hmmm. If you normally vape VG with very small amounts of flavouring, why dissolve the malic acid in PG?
Why not dissolve it in a minute amount of PGA (if needed*) and then in water** or VG?
But if something makes you cough, the easy solution is DON'T VAPE THAT.
For some unfathomable reason EM seems to irritate my throat - hence I won't be putting EM in anything I vape a lot of.
And repeating/recapping my rant from earlier:
Just because I happen to get some kind of adverse effect from something doesn't mean that it isn't generally safe (I'm a specialist in developing very unusual but theoretically plausible side-effects to medications, this doesn't mean those medications are unsafe or bad or dangerous *in general*, it just means they aren't a good fit for *me*).
And vice versa, just because something is generally thought of as healthy or effective is no guarantee it will be good or effective for everyone (when it comes to pain meds the tylenol-type (acetaminophen/paracetamol) does squat for me, as did the only opiate I've ever been prescribed - this doesn't mean tylenol or opiates are worthless, it just means that for *me* I'll be sticking to aspirin and other NSAIDs).
* So far I've had zero problems with dissolving TA, EM and menthol by using this method: Put a suitable amount (ie tiny for TA, and to taste or according to a recipe for EM and menthol) into a bottle. Pour in as little PGA as you can. Shake vigorously/heat. When it's dissolved or nearly dissolved, add PG or VG to make up the colume specified. With this method even my TA is completely clear, and hasn't left rings on any bottles so far.
There's really very little PGA needed, but especially for mixing with VG I've found it really helps a lot.
** Water because that probably makes it easier to calculate the strength of your acid.