A little bitter mouth may be caused by oral diseases, liver and gallbladder diseases, digestive system diseases, emotional factors, etc. It is recommended to go to a regular hospital and consult relevant professionals. 1. Oral diseases: for example, oral ulcers, periodontitis, not paying attention to oral hygiene, etc., will lead to bad breath, bitter mouth and other problems. 2. Liver and gallbladder diseases: common cholecystitis, gallbladder stones, etc. lead to abnormal digestion and excretion of bile, which can further lead to a bit bitter mouth. 3. Digestive system diseases: when patients have indigestion, bile reflux and other diseases, it may also lead to a bitter mouth. 4. Mental factors: when the mental stress is too high, the quality of sleep is not good, may stimulate the nervous system function change, may also appear mouth a little bitter. Usually pay attention to oral hygiene, relax your emotions, keep a good night’s sleep, avoid exertion, if the symptoms are difficult to relieve, or other discomforts, you should consult a doctor in time.