The licking can cause the blister, actually, especially if it is now bleeding. I have had this same problem with my dog several times. All I can tell you is that you HAVE to try to stop your dog from licking his paw. We had to do it with the help of the vet. They gave us prescription pills that were a type of steroid to stop the itching/pain. They gave us prescription pain pills, and also a tranquilizer to make her sleep more than lick. Some dogs can take Benedryl pills and it will help them to stop hurting and make them sleepy. However, my dog reacted oppositionally to this and went hyper, so use with caution.
