The reasons for the foul smell of the breath include the following: 1. When deep cavities are formed in the teeth, a large amount of food residues accumulated in the decomposition of bacteria emit a putrid smell. 2. 4, suffering from gastric ulcer, duodenal ulcer and other digestive system diseases, can occur digestion, malabsorption, often appear acid reflux, belching and other phenomena. 5, diabetic patients do not pay attention to diet control, resulting in acidosis, exhaled gas has a foul smell.