Simple answer, 80% of the reasons for bad breath is the problem in the mouth, such as periodontitis, wisdom teeth, pulpitis, dental caries, calculus and so on, most of them are the kind of bad smell, the specific taste is like a faint smell of rotten eggs. The specific reasons are divided into several: a. Oral diseases caused by bad breath for common reasons. Some people find dental disease in the mouth because of bad breath, these recommendations in the Department of Dentistry, perfect treatment of intraoral diseases can often improve bad breath. Second, food residues cause bad breath. Some people often plugged teeth, the best way to get rid of food debris is to use dental floss, rather than toothpicks. If you have flossed once, the sense of accomplishment of hollowing out the teeth is far more than a toothpick. After each meal with dental floss will be strangled once each tooth gap, and then rinse, you can basically solve the bad breath caused by food debris. Third, less saliva caused by bad breath. Some people have bad breath in the morning together with the opening of the eyes, after the good, this is because of less saliva secretion when sleeping, the mouth of the anaerobic bacteria increase, corruption and necrosis caused by this situation does not require special treatment, a mouthful of water will be good naturally. But for some elderly people, because of high blood pressure or other diseases, oral medication caused by reduced saliva secretion, you need to drink water often, to keep the mouth moist. Fourth, tongue moss caused by bad breath. Some people can be seen on the back of the tongue yellow tongue moss, especially the part of the tongue root, tongue moss below the accumulation of a large number of anaerobic bacteria, you can brush your teeth at the end of the tongue as far as possible outward, using a toothbrush (no toothpaste) gently brush off the tongue moss outward, do not have to pursue too clean, because the tongue root mucosa and some contour papillae are more fragile, too heavy brush will damage these tissues. Five, tonsil stones caused by bad breath. These are tonsil crypt, long-term obstruction, poor drainage of secretions, resulting in small stones, which occasionally fall off on their own from the mouth spit, this stone has a foul smell, can generally be removed, for stubborn stones, you can also choose to remove the tonsils. Sixth, other causes of bad breath. For example, sinusitis, runny green nose, this belongs to the bacterial infection, wait until the end of the bacterial infection to get well. For gastrointestinal diseases resulting in bad breath, often more serious diseases, need to be seen in the gastroenterology department, reasonable diagnosis and treatment.