Bad breath is an unclean odor emitted from the mouth when breathing. In modern society, bad breath has become one of the reasons that affect people’s normal social life, and many people carry a heavy psychological burden because of bad breath. Under normal conditions, there is sometimes an unclean odor in the mouth. This odor is because the person did not eat and drink after a night’s sleep, resulting in a bad taste in the mouth after waking up in the morning; or it is caused by eating vegetables or other foods containing sulfur substances. Such odor lasts for a short time and can be quickly eliminated by proper oral hygiene measures. Pathological bad breath, on the other hand, is caused by disease, pathological states or tissue abnormalities in the oral cavity. Non-oral halitosis is caused by some other diseases, such as: respiratory diseases, nasopharyngeal diseases, digestive system diseases, etc. The problem of bad breath can only be solved after the eradication of diseases in the body. The most common bad breath is orogenic, accounting for 80%-90% of halitosis, mainly caused by anaerobic bacteria. Bacteria in the mouth decompose oral residues through spoilage, producing volatile sulfides and other substances that produce bad breath. The common causes of bad breath are poor oral hygiene, large accumulation of plaque and calculus, caries, gingivitis, periodontal disease, etc. Some people do not pay attention to oral hygiene and cannot brush their teeth properly on time, resulting in a large accumulation of plaque and calculus and a thick tongue, which can easily cause bad breath. And periodontal inflammation not only has a large accumulation of plaque and a significant increase in the proportion of pathogenic bacteria, but also leads to a significant increase in the amount of bacteria in the back of the tongue and saliva, and these are the main reasons for the formation of bad breath. Also tooth remnants, crown remnants and bad restorations are important causes. Some people are not willing to go to regular dental hospitals for treatment such as fillings and veneers, but choose street dentists, who make dentures with many bad designs due to technology and materials, which cause damage to the gums or lead to the accumulation of food residues and induce bad breath. There is no need to cause great psychological stress due to bad breath, but it is not right to take it lightly. It must be clear that bad breath is a pathology that is dangerous to oral health because it produces gases that are volatile sulfides and can be toxic to periodontal cells. In addition, sulfide can increase the permeability of the mucosa, making it easier for toxicity to penetrate the mouth and aggravate other lesions, so patients with bad breath should undergo symptomatic treatment as early as possible. To prevent bad breath, you should brush your teeth with fluoride toothpaste every day in the morning and evening and after eating, and at the same time floss carefully to clean the interdental space. Brushing should also be accompanied by attention to brushing the tongue and upper jaw in the correct way. If you have dentures, you should clean them properly every day and remove them before going to bed. Drink plenty of water every day to keep your mouth moist. Also avoid eating strong tasting foods. When you notice that you have bad breath, you should seek medical attention and actively search for the cause. Patients with bad breath are recommended to receive regular oral examination. Treat caries, periodontal disease, dry mouth and mucosal disease to improve oral hygiene.