Propylene glycol is used in many liquid medicines, including codeine linctus and many others, which are drank in large amounts. It's also used in e-cigs, in much lesser amounts, but is inhaled. It's used in fog machines and a few other things. PG is totally fine to ingest, in ml amounts. Even isopropyl alcohol is fine as a solvent, if only very small amounts are used. It smells and tastes like nail polish remover, but it works. A drop of water makes things dissolve better in isopropyl alcohol. I've done this several times, with various things that should dissolve, but don't. It's very odd. Does anyone know why?