Bad breath is generally not contagious. The most common cause of bad breath is periodontitis, a disease of the soft tissues surrounding the teeth, which is caused by plaque adhering to the teeth and irritating the periodontal tissues, and plaque is the initiating factor in periodontitis. Patients with bad breath will have a large amount of calculus as well as plaque in their mouths. This breeds a lot of harmful bacteria and causes bad breath. When bad breath is caused by periodontitis, the main thing that needs to be done is regular treatment of periodontitis. The main way to treat periodontitis is basic treatment, mainly plaque control, is to use brushing to control plaque, to master the correct method of brushing, to develop a good habit of brushing, but also with the use of dental floss, interdental brush and flosser, so that you can well control plaque. Supragingival scaling is the use of ultrasonic vibrations to remove calculus and plaque from above the gums around the teeth. Subgingival scaling is the manual removal of calculus and plaque below the gingiva around the teeth. This is combined with local rinsing, medication and the application of mouthwash so that periodontitis can be treated well. For bad breath caused by periodontitis, the bad breath will slowly disappear after the periodontitis is treated and maintained. Bad breath is generally not contagious, mainly caused by oral diseases, must be thoroughly treated oral diseases.