Bitter mouth at night may be due to bile reflux, or it may be related to other factors such as dietary influences, oral diseases and respiratory diseases. 1. Bile reflux gastritis: During an attack, bile mixed with gastric contents refluxes into the upper gastrointestinal tract or the mouth, which can trigger the symptom of bitter mouth at night. 2. Dietary influences: Consuming more bitter melon, bitter chrysanthemum and other foods at dinner time can also trigger bitter mouth at night. 3. Oral diseases: such as gingivitis, periodontitis and oral ulcers can lead to abnormal secretions in the affected area, which in turn can lead to the symptoms of bitter mouth at night. 4. Respiratory diseases: such as chronic pharyngitis, purulent tonsillitis, etc., the affected area of the secretion mixed with saliva, can also trigger the symptoms of bitter mouth at night. This nighttime bitter mouth phenomenon, it is recommended that patients should seek medical attention as soon as possible to clarify the cause of the disease, and to be targeted treatment.