Bad breath is a common phenomenon in people’s life and has various causes. It is mainly caused by local factors in the mouth such as cavities, calculus, deep periodontal pockets and systemic diseases such as blood disorders or digestive diseases. Bad breath is treatable. If it is caused by local oral factors, plaque, calculus, treatment of dental caries, pulp necrosis, periodontal disease and other pathogenic factors should be removed, in conjunction with drugs such as 3% hydrogen peroxide rinse, 0.1% chlorhexidine rinse. If it is secondary to systemic diseases, we should first actively search for the cause and carry out effective treatment, and the bad breath will disappear naturally.