Bad breath can he associated with gingivitis and dental abscess or tonsillitis and pharyngitis. It can also be a sign of metabolic diseases (diabetes mellitus, kidney and liver disorders), respiratory illness (upper respiratory infections, pneumonia), gastrointestinal diseases and immune-mediated disease. Almost any severe illness, like infections (viral, bacterial, fungal) or cancers, can affect mouth odor regardless of their actual location.
Diet is also important and can affect breath in many ways. A pet might consume decomposing debris in your yard, its own stools or the feces of other animals. Malnutrition and related vitamin or mineral deficiencies can also cause bad breath. Halitosis can also be the result of self-grooming, for example, if your pet has an anal sac infection or lower urinary tract disease.
If your pet has bad breath, it is important to find out why. Although a variety of products are marketed to mask mouth odor, these items are usually ineffective.