Bad breath can be caused by Helicobacter pylori infection, or it can be caused by other reasons, such as indigestion, mouth ulcers, chronic pharyngitis and so on. 1. Helicobacter pylori infection: after being infected with Helicobacter pylori, it is easy to break down some substances to produce ammonia, which leads to bad breath. 2. Indigestion: As food is not digested thoroughly after entering the gastrointestinal tract, it will ferment in the intestinal tract and produce odor, thus causing bad breath. 3. Mouth ulcers: mainly due to the ulcers wound easy to breed all kinds of bacteria growth, which produces bad taste, resulting in bad breath. 4. Chronic pharyngitis, laryngitis, sinusitis, etc. may also lead to bad breath, unrelated to H. pylori. Bad breath may also be caused by other reasons, such as dental caries, gingivitis, etc. It is recommended to pay attention to oral hygiene, if bad breath still exists, it is best to go to the hospital in a timely manner, with the doctor to take the examination and treatment.