There are a number of causes of bad breath in dogs. It is important to evaluate the source of the bad breath, as each cause has a different, appropriate treatment approach.
Instructions
Sources and Cures
Sometimes bad breath in especially older dogs comes from the fact that teeth have not been properly looked after. The first step if you suspect this is to have the dog's mouth examined by the vet, who will probably want to clean the teeth. He will usually give you some oral rinse to use at home for preventive care, and may suggest you actually "brush" your dog's teeth, using one of the specially made tools, or a soft brush. Also, teeth will stay cleaner, and thus reduce mouth odor, if dogs eat primarily dry food, and eat crunchy treats, as it helps remove tartar. Some treats also contain odor retardant ingredients themselves.
Sometimes a symptom of ill health can be bad breath also. Your vet can diagnose this and properly treat the condition causing the odor, which should eliminate it.
Bad breath may also be caused by what the pet is eating. Certain dog foods or table scraps may cause it, and a change of diet may eliminate the odors. How a dog reacts to food is different with every dog, so you must evaluate this based on your pet, not on general information you may have.
It may also be caused by digestive problems, in which case digestive enzymes made for canines may be in order. You can obtain digestive enzymes from your vet or online, with your vet's supervision and approval.
For general bad breath (from no serious, discernible cause), natural remedies work best, and in some cases, mirror what we ourselves can use. Some people make their own dog biscuits, containing only natural ingredients, including parsley, often eaten by humans for halitosis. There are a number of products out there also, including chew toys, which have natural ingredients that help with the bad breath problem. You can buy mouth rinses also for dogs with this problem, and there are dental flosses and swipes available from many vendors as well.