Clean it with some hydrogen peroxide and then take him to see your vet. It could be any number of things. I just had my dog in this morning for something similar. She said that it looks like he may have gotten bit by some
what it is. He is on Prednisone and Clindomyacin and they are not working. He is also constantly licking his left front paw. Opensore on the left upper lip and now it is starting on the other side. The vets have no idea...
Cold Sore Symptoms – Caring For Cold Soresby
on the surface end of a nerve. When the sore is open, it exposes those nerves.
You are most contagious... FINALLY STARTS.
The damage is done once the soreopens up. You will notice improvement every day...