Bad breath is a symptom, which can be caused by the following reasons: firstly, it is caused by inflammation of the mouth and nose, such as atrophic rhinitis, sinusitis, gingivitis, chronic tonsillitis and so on; Then there are digestive system diseases and some systemic diseases, such as diabetic ketoacidosis and uremia. At this time, bad breath varies with different diseases. Each has its own special smell. In other cases, some individuals lack certain digestive enzymes, which leads to indigestion in protein, or bad oral hygiene habits and eating habits, resulting in bad breath. This is simple bad breath. In fact, the first two situations show not only bad breath, but also simple bad breath. As long as we find the root cause, we can treat the primary disease according to the condition and the cause of bad breath.