Bad breath like fecal odor is not necessarily a sign of cancer, but may also be caused by other reasons, and should be treated on a case-by-case basis. If patients do not pay attention to oral hygiene and do not clean their teeth, microorganisms in the mouth will continue to grow in an anaerobic environment, which will cause the residual food in the mouth to ferment and produce an unpleasant odor, and then bad breath will be formed. In addition, tooth decay, periodontal abscess, gingivitis, etc. can also lead to bad breath, and in serious cases can be similar to the odor of stool. Gastrointestinal digestive disorders, gastrointestinal diseases or consumption of unpleasant smelling food can lead to bad breath. Generally, bad breath can be relieved by improving diet, oral hygiene, and treating the cause of the problem. However, if the patient’s mouth smells very bad, it is necessary to be alerted. For example, patients with gastric cancer often have the smell of rotten duck eggs in their mouths, patients with lung cancer can have the smell of rotten fishy breath, and patients with nasopharyngeal cancer, tongue cancer and other tumors can also have bad breath. Therefore, when patients have bad breath, they can go to the gastroenterology department for corresponding examination, and after clarifying the cause, they can undergo symptomatic treatment under the guidance of professional physicians.