Bad breath in dogs can be a symptom or sign of a health problem. The main cause of bad breath is the presence of dental plaque (sticky film on the teeth) and the deposit of tartar on the dog’s teeth. To remedy this, limit wet foods, brush your dog’s teeth every day if possible or give special kibbles to improve your dog’s oral health. Other than that, it can be a sign of a general disease such as fungal infections, kidney disease, diabetes. In every case, you might consider going to a Veterinarian.