Waking up with a bitter and smelly mouth may be related to dental caries, periodontitis, gastroesophageal reflux and other reasons. 1. Dental caries: food debris stays in the cavity for one night, and under the action of bacteria, food corruption can occur, leading to a bitter and smelly mouth after waking up. 2. Periodontitis: when the virulence of pathogenic bacteria in dental plaque is too strong, the protective effect of the body is not enough, or the immune system overreacts, it can cause inflammatory reaction, which can lead to bad taste in the mouth, pus between the gums and teeth, and so on. 3. Gastroesophageal reflux: the stomach contents containing bile, stomach acid and other components of the role of bacteria to appear corrupt flavor, if its backflow into the esophagus, can cause the mouth bitter, odor. It is recommended that those who wake up with a bitter and smelly mouth go to the hospital in time to clarify the cause of the disease and standardize the treatment under the guidance of the doctor.