The most common causes of bad breath are oral diseases and digestive system diseases, and the corresponding treatment should be done according to the specific diseases. 1, oral diseases: oral diseases most likely to cause bad breath is caries and periodontitis. In the mouth of patients with bad breath, there will be a large amount of plaque and calculus, so it is easy to cause caries and periodontitis. Once you have caries or periodontitis, it will cause bad breath. The presence of a large number of harmful bacteria in the mouth will produce oral odor. So usually you must do a good job of oral hygiene protection, so as to prevent the occurrence of bad breath. To develop a good habit of brushing teeth, master the correct method of brushing. Usually you can use some mouthwash to sterilize the mouth and prevent the growth of harmful bacteria in the mouth. 2, digestive system diseases: digestive system diseases, mainly refers to the gastrointestinal tract diseases. These diseases can cause the occurrence of bad taste in the mouth. To specific to the gastroenterology examination, once the presence of digestive system diseases to be treated in a timely manner, so as to remove the bad breath caused by digestive system diseases. Once bad breath occurs, it is important to go to the hospital for a timely examination. To specifically find out the cause of the disease, so that the cause of the disease to do the appropriate treatment.