PG/VG facts

   PG and VG (Propylene Glycol and Vegetable Glycerine) aren't actually additives, they are the base of the liquid to which flavor and nicotine are added.
   In a proper juice the only ingredients should be : PG/VG (you can adjust the ratio of the two depending on personal preference, and you can even go 100% of either one) Flavoring (USP-grade only! That means it is safe for human consumption) and finally, nicotine (the lower the level the better in my opinion, I vape at 18mg , but i am weaning myself off with the step down system. Some companies add color to their juice, and so long as those colors are food-safe/ USP-grade there will be no health risk there.
                                 Now for the safety of inhaling PG/VG:
 PG is the "ultra-scary antifreeze" that is in all these juices, except for the fact that PG is specifically used as an anti-freeze because it is non-toxic. In fact, PG vapor is sprayed in hospital operating rooms (while people are in the rooms) every day because PG has anti-bacterial properties. Surgeons breathe in PG Vapor every day!
Now for VG, VG is a simple polyol (sugar alcohol) compound. It is a colorless, odorless, viscious liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids known as triglycerides. Glycerol is sweet-tasting and generally considered non-toxic.
  So non-toxic = safe too me that is all that matters.