Getting up in the morning with a bitter mouth is related to poor hygiene habits, nerve dysfunction, oral and nasal diseases and systemic diseases. 1. Poor oral hygiene, food residues in the role of bacteria to produce acid, will lead to bitter mouth. 2. Excessive mental stress and lack of sleep cause nerve dysfunction, which can lead to bitter mouth. 3. The presence of caries, periodontal disease or inflammation of periapical disease will not only cause bad breath but also bitter mouth. Nasal diseases that lead to open-mouth breathing and bacterial infections can also cause bitter mouth symptoms. 4. Systemic diseases such as liver and gallbladder diseases, gastrointestinal diseases, diabetes mellitus, renal disease, bile reflux, etc. may also cause bitter mouth symptoms. Therefore, bitter mouth is mostly seen in the above conditions, you can go to the stomatology department or gastroenterology department to find out the cause of the disease and symptomatic treatment.