Usually bad breath is not contagious, there are many causes of bad breath, and the possibility of indirect transmission from other causes cannot be ruled out. Bad breath is a common oral disease, can be caused by unclean eating habits, such as not cleaning teeth, so that the mouth microorganisms in an anaerobic environment, the mouth residual food fermentation produces volatile sulfide, sulfide smell is more unpleasant, thus forming bad breath. This kind of bad breath is usually not contagious, and the bad breath can be gradually relieved after good daily cleaning. Gastrointestinal diseases, such as chronic gastritis, gastric ulcer, etc. can also cause bad breath, but is not contagious, after active treatment of the original disease can reduce bad breath. However, if the patient has more bacteria in the mouth, such as Helicobacter pylori, through close contact, it is possible to make the other side of the mouth of such bacteria, if the other side usually do not pay attention to their own oral hygiene, the increase in the reproduction of bacteria in the mouth, thus causing periodontitis, dental caries, etc., there will be bad breath symptoms. Patients with bad breath should pay attention to oral hygiene, brush and rinse their teeth after meals, and go to the dentist regularly for dental checkups to detect dental diseases early and treat them early.