Ask a Dog Vet and Get Answers to Your Dog Veterinary Questions
I am sorry to hear you are worried about Rambo. My name is Rebecca. I am a veterinarian and will do my best to help.
How long has this red swollen area been there? Is it painful for him?
If it smells bad, it is probably infected. The roots of the back molars extend to just below the eye, and we see a red raised area just below a dog's eye if a tooth is infected. Here is an article, with a drawing of where you see an infected area on the face if a dog has an infected tooth:
Was he born just this past March; is he a puppy? A tooth root infection is less likely, but it could be some other type of infection. The bad smell makes infection the most likely thing. You can apply Neosporin to the area, and cortisone ointment (Cortaid, Cortizone 10) to the area, but he may need to get antibiotics from your veterinarian.
Is he eating normally? Does he seem painful?