Bad breath caused by tooth decay may be caused by rotting and deterioration of food residues, or by decay and deterioration of teeth; symptomatic treatment is required, please follow the doctor’s instructions. 1. Since cavities are usually deep and large, food residues are easily embedded in the cavities and are difficult to clean with toothpicks; when food residues rot and deteriorate, they may produce a very foul odor. However, it is not excluded that tooth decay itself causes tooth decay and deterioration, resulting in a bad odor. 2. For tooth decay, filling treatment should be carried out on the basis of removing the decayed material. If the cavity is deep and does not involve the pulp, the pulp-protecting material should be put into the bottom of the cavity and then filled; if the cavity involves the pulp, root canal treatment should be carried out under local anesthesia, and then filling of the cavity should be carried out. Bad breath caused by tooth decay should be consulted in time, and the doctor will give targeted treatment after clarifying the cause of the disease.