There are several possible causes for bitter mouth and bad breath: 1. systemic diseases, such as hepatitis, cholecystitis or gastrointestinal diseases. 2. poor oral hygiene, such as a large amount of plaque, calculus or a large number of dental caries in the mouth, can easily cause bad breath. 3. 3, wake up mouth bitter, and bad breath may also be caused by mental factors, such as poor mental state, long-term stay up late, this situation is likely to cause bad breath. 4, due to a hangover or eat spicy, irritating, odor heavy food, may also wake up mouth bitter or bad breath, such as eating stinky tofu, garlic, chili, etc., this situation may cause the next day mouth bitter or bad breath. In this case, it may cause the phenomenon of bad breath the next day.