Bad breath like stool may not necessarily be a sign of cancer, but may also be caused by other reasons, so patients need to analyze each case individually. If the patient does not pay attention to oral hygiene, does not brush and rinse the teeth on time, resulting in food residues remaining in the mouth, the fermentation of the residues will produce an unpleasant odor. If the patient has tooth decay, periodontal abscess, gingivitis, it will also lead to bad breath, and in serious cases, the mouth can smell like stool. If patients have gastrointestinal diseases or usually like to eat onions, garlic and other irritating food, also easy to cause bad breath. However, if the patient’s mouth often smells like rotten duck eggs, he or she should be alert to the possibility of stomach cancer; in addition, if there is a rotten smell in the mouth, he or she should be alert to the possibility of lung cancer. It is recommended that patients should go to the gastroenterology department of the hospital for examination in a timely manner to clarify the cause of the disease and then carry out symptomatic treatment under the guidance of professional physicians. In addition, patients should develop good living habits, brush their teeth at least twice a day in the morning and evening, avoid smoking and drinking, and avoid spicy and stimulating food.