I have mixed emotions about this question. There are a lot of vapers that have been vaping heavily since eCigs were invented. That is about 7 years. So far, we have not heard of one person getting ill from vaping. That person, if they exist, is the one that the FDA, ALA, the ANTZ, and every other alphabet soup agency or advocacy group has been looking for. If he or she exists, we WILL know their name the same day that they are diagnosed. This person is the holy grail of the anti vaping community.
- We know for sure that long term inhalation of nicotine at acceptable levels is not harmful.
- The effects of inhaling PG vapor have been studied for decades, and there are no harmful effects.
- The effects of inhaling VG vapor have not been studied as fully as PG, but there haven't been any serious claims that inhaling VG vapor is bad for you. From what I can tell, the scientific community believes that that VG is so inherently safe, and that the human body processes it so easily and efficiently, they won't even bother to study it any further.
The film on the windshield must be VG. I believe that the heaviness in the lungs is also the VG. Vaping VG simply turns the liquid VG into droplets which probably turn back into liquid VG when the droplets come into contact with each other when you inhale them. This causes the heavy feeling some experience. Chemically, the VG liquid in your lungs and throat is safe. Obviously, too much of any liquid in your lungs is not good. This is why I have not considered heading in the max VG direction. I just think that it would not be good for me.
I'm conflicted on the diacetyl issue. Regular cigarettes have it in them, but we know that smoking kills. The diacetyl may be a contributing factor in that (or a major one, or the actual reason). There are so many bad things in cigarette smoke that I don't think that even the people who have been studying it can say for certain which compounds, or combinations of, are actually doing the killing. Maybe all of them. The popcorn factory folks were in a completely non comparable situation from vapers. They had exposure to much higher concentrations for much longer periods of time. There aren't many people on the planet that will experience similar levels of exposure. What we really haven't seen is people getting diacetyl poisoning (or whatever the disease would be) from vaping, or other exposures to diacetyl. In 30 years, we may just find that vaping diketones has no impact at all since all of the molecules are suspended in VG and simply don't manage to get as deep into lung tissue as it does when you inhale them in steam, or in a cloud of dry powder. Of course, we may find that vaping 2ml per month of eliquid containing diketones is lethal after 30 years. We probably will not ever know for sure. 99% of all vapers' health has already been impacted to some degree by smoking prior to when they started to vape. To be able to accurately determine the effects of vaping diketones, we would need to test by having someone who has never smoked vape diketone laden juice for a couple of years before we would be able to get a clean test.
I honestly believe that vaping unflavored (PG/VG/Nicotine) is 100% safe if the ingredients are not contaminated. I believe that vaping flavors that have no diketones is about 95-99% safe, and I believe that vaping flavors with diketones is probably in the ball park of 80-90% safe (unless you sub ohm an ounce of it every day for years on end). I believe that DIY is somewhat safer than B&M eliquid solely because the mixer is also the user, and we are generally more careful making things that we intend to consume ourselves.
I am 50 years old, and I smoked for just shy of 30 years. I have been a non smoker for 54 weeks now. I could feel the effects of my smoking, and I have no doubt that I was going to have a smoking related illness at some point down the road if I did not stop. In my one year of vaping, I feel so much better that I no longer believe I will die because I smoke. If vaping causes me any negative health effects, I'm fairly confident that it will be 2 decades or more before that happens, as I consume less than 4 ml on any given day. At 70, that should be the least of my worries.
100% safe? Probably not. More than 80% safe? I believe that to be the case. DIY safer than pre-made? Most likely.