"Doggie breath" most often refers to an unpleasant odor coming from a dog's mouth. There are several causes for "doggie breath" some of which can be relatively normal for a particular dog to abnormal and associated with tooth or mouth abnormalities.
Problems such as inflammation of the gums, abscessed teeth, bone or hair caught in the mouth, oral ulcers, or tumors in the mouth can all cause bad breath. Kidney failure and lung tumors can also alter breath odor.
If your dog has bad breath, have him examined by your veterinarian to determine if there are any underlying health problems. Depending on the underlying cause, the cure may be as simple as a dental cleaning or routine brushing of the teeth.
Halitosis is the term used to describe bad breath in dogs. For more information, please read Halitosis in Dogs