Bitter mouth may be caused by physiological factors such as bad habits, or it may be related to oral diseases and digestive system diseases. 1. Physiological factors: If you have recently had a poor diet, overeating, excessive mental stress, lack of rest, and poor oral hygiene, your mouth may always be bitter. 2. Oral disease: the mouth is always bitter may also be related to oral disease, such as the existence of dental calculus, gingivitis, as well as mouth ulcers and other diseases, may also appear in the mouth is always bitter situation, usually may be accompanied by pain and other discomforts. 3. Digestive system diseases: Bitter mouth may also be related to digestive system diseases, such as reflux esophagitis, gastritis caused by Helicobacter pylori infection, as well as bile reflux, cholelithiasis and so on. There are many reasons why the mouth is always bitter, and it is recommended to seek timely medical treatment after eliminating physiological factors so as not to delay the condition. At the same time, attention should be paid to a reasonable diet, maintain oral hygiene.