Bad breath in the morning may be related to poor oral hygiene, oral diseases, gastrointestinal diseases and other reasons. 1. Poor oral hygiene: If you don’t clean your mouth before going to bed, the food left in your mouth will ferment at night, and you will have bad breath in the morning. 2. Oral diseases: such as dental caries, due to food residues left in the cavity, under the action of bacteria and other microorganisms, can produce an unpleasant odor. 3. Gastrointestinal diseases: such as gastritis, gastritis patients have reduced digestive capacity, so that the food eaten the day before stays in the stomach for a long time, after fermentation to produce a bad smell, may appear in the morning bad breath. It is recommended that people with bad breath in the morning get up and see a doctor in time to clarify the cause, and if treatment is needed, it should be standardized under the guidance of a doctor.