It looks like a eucinophilic granuloma, commonly called a "rodent ulcer." Take kitty to the vet, he or she might need a run of antibiotics or steroids.
I can't really tell bkitty, the photo is quite unfocused...I see its on his lower jaw, but you say its red and blister like...so that doesn't sound like feline acne..I really don't know, it would have to be examined by a Vet I'm afraid....is it possible he got burned off something????? sorry can't be of more help.-(