[Petite]

It looks quite sore, which is presumably why he doesn't like you touching his face. It does sound as though it has been caused by consistent bar chewing. Could you see how it goes in the next few weeks now he isn't bar chewing? All might be well and he may not need a vet visit - unless you want to get something to apply to promote healing (although you may already have something like that to hand). Joe sounds happy enough in himself now he's able to do normal hamstery things.