The important point about PG is, the individual that's ingesting it. Considering the massive quantities one must eat before its toxic, one might generally say that its safe. However, that's not to say the certain individuals aren't sensitive to it or worse, allergic. As for myself, one month into vaping, I've found that PG is way to irritating. This has lead me to vape 10% PG / 90% VG. I'll also add that I did a brief test, vaping 100% PG to find out if in fact this was what was bothering me about my e-juice (and it was). Oh and, do you know what 100% PG smells like? Cold cream skin moisturizer. As a child I had allergic asthma and would gag on the smell of cold cream. So, the bottom line is, there's no one safety answer to apply to everyone.