While I appreciate your confidence in us here on the forum, it would be inappropriate for us to try to diagnose the issue online: we aren't even seeing the animal
in question, & you'd be surprised how differently people often describe the very same things, whether symptoms or colors or sizes... You might be right, that it's
some sort of bacterial infection...or what about a burn? Anyway, you really need the help of a vet, ok? All the best...let us know how things turn out?
And if you need some options for the right vet, try this:
https://arav.site-ym.com/search/custom.asp?id=3661
(The other thing we aren't seeing or getting here is all the necessary information about his caging.)