I am now in my eighth week of vaping and only in the last week, since I started adding additional VG to all my juice, have I noticed a vaping related increase in SOB. I stopped using the juice I had added VG too a couple of days ago and have immediately noticed an improvement in breathing. I have early stages of COPD with constant SOB so I am very sensitive to any and all changes in my breathing. I don't know if this increase in SOB is an allergy to VG or a common symptom but I suspect it is just a common symptom. If you look at most Material Safety Data Sheets for Glycerin (see
http://avogadro.chem.iastate.edu/MSDS/glycerine.htm ), you will notice under Potential Health Effects the warning "Inhalation of a mist of this material may cause respiratory tract irritation", and I am fairly certain this is the effect it had on me.
PG, on the other hand, has been a God Send to me. A side effect of some of the meds I take for hypertension and COPD is Dry Mouth. Before I started vaping I had cases of extreme dry mouth. I would awake at night about every thirty minutes to an hour with my palate and throat in agony due to dryness and have to sip some water before I could go back to sleep. The only thing that helped any with the dry mouth was PG based mouth sprays like Biotene. Since I started vaping I now am able to sleep straight through the night without waking from dry mouth. I attribute that to the PG which coats my mouth and throat when vaping much like the Biotene mouth spray, except the mouth spray only lasted two hours and the coating from vaping lasts at least eight.
Overall, except for the VG incident, my COPD has noticabley lessened since I started vaping. I was wheezing badly before I started vaping, and scarcely had any wheezing while vaping until my lungs became irritated by the VG. I am really bummed about the effect VG has on me because I love the vapor you get with VG. So, I am just going to vape PG juices and let my lungs heal some. Vaping PG makes my lungs feel good as if it were actually therapeutic. Who knows, it may be! At least for me. PG is antimicrobic, capable of destroying or inhibiting the growth of microorganisms, which to my understanding VG is not. The VG mixes I had a reaction to were 70/30 PG to VG mixes, so I am going to try 80/20 and 90/10 before totally giving up on VG.
P.S.: I was able to quickly eliminate the possibility of flavors causing the SOB because every day juices I had no problems with increased SOB shortly after I added the VG.