There is no sugar (sucrose) in any
juice I know of.
Some juices use various sweeteners: sucralose, stevia etc. might have some theoretical risks if they actually break down, but they shouldn't unless you dry burn juice residue. Another common sweetener used is ethyl maltol. In any event, risks of inhaling the flavorings are not established - i.e. no one knows what / if there are risks. Some flavors are known to be risky - i.e. diacetyl which is a "buttery, custardy" flavor - and they are avoided by juice makers, but you might ask specifically for juices that taste like butter.
