The odor of bad breath may be due to the existence of food residue in the mouth that has not been cleaned up for a long time, probably the wisdom teeth or the teeth of the teeth located in the inner part of the teeth are difficult to get a thorough cleaning by ordinary brushing, and the residual food residue in these places will be fermented and decayed for a long time, and the odor similar to bad breath will occur. It may also be due to the existence of dental caries, dental caries is a cavity on the teeth that has been eroded by the bacteria of dental caries, which may be large or small, but once there is food residue in the cavity, it is more difficult to clean the cavity by brushing only. And as the bacteria continue to erode the food residue, the odor of decay will be slowly emitted.