There are several possible causes of bad breath: 1. poor oral hygiene, a large amount of dental calculus and plaque in the mouth, and the phenomenon of pus in the gums, or it may be due to a large number of dental caries in the mouth, which is particularly prone to oral odor and can feel the phenomenon of bad breath when breathing. 2. bad breath may also be caused by gastrointestinal tract dysfunction, possibly due to liver and gallbladder diseases. 3. The smell of breath may be caused by systemic diseases, such as hepatitis, cholecystitis or gallbladder stones, etc. 3, caused by endocrine disorders, such as unstable blood sugar, blood pressure or unstable heart function. 4, the smell of breath may be caused by the infection of Helicobacter pylori. 5, the smell of breath may be due to long-term late night, eating smelly food, such as stinky tofu, garlic, onions, chili peppers The odor may be produced by eating bad food for a long time.