It's PG and VG and flavor. PG breaks down into lactic acid and VG into sugar. So, it can cause some issues like a build up of said lactic acid and give you unusual muscle cramps (if you do this a lot or are especially sensitive). The VG may have consequences, much like consuming loads of sugar does regardless. Drinking an extra couple of glasses of water daily will certainly help (it'll help even if you don't vape, most people just don't hydrate enough) and if you notice yourself developing changes, stop and see if they clear up. I'm not really sure what long term consequences it can have, but my general belief is they will not develop over night, are not extreme and are probably reversible on the whole if you just stop when you notice things like the cramping. Most people don't even get it, but it's been reported.
I'm no scientist, this is just imo.