”When you enter the abalone restaurant, you do not smell the stench for a long time”. This shows that human’s own olfactory system has a strong adaptability. For their own bad breath, with the passage of time is less likely to be detected by their own olfactory system, often because of the rejection or reminder of the people around them before they become aware of it, so in foreign countries is imaginatively called “social cancer”, is a cancer in human interaction, unspeakable hidden disease. Halitosis is an unpleasant odor emitted from the mouth, also known as oral odor or bad breath, and the international standard classification of halitosis was officially established at the third meeting of the Vancouver International Halitosis Forum on March 13, 1999. This classification standard follows the basic principles of halitosis treatment needs and divides halitosis into three main categories, namely, true halitosis, pseudohalitosis and halitophobia. Among them, true halitosis is divided into physiological halitosis and pathological halitosis. The vast majority of the people believe that bad breath is caused by digestive disorders, and this understanding has been around for a long time. But with the professional investigation is seriously inconsistent: 90% of the factors of pathological halitosis from the oral cavity, known as orogenic halitosis. Orogenic halitosis is mainly due to the oral cavity microorganisms, especially gram-negative anaerobic bacteria breeding, decomposition, producing a large number of volatile sulfide (hydrogen sulfide, methyl mercaptan, etc.), other volatile organic compounds (ammonia, dimethylamine, trimethylamine, alkanes and benzene derivatives, acetone, etc.). Among them, the higher the concentration of sulfide, the heavier the odor. The causes of orogenic halitosis include periodontal disease, thick tongue, food impaction, caries (especially adjacent surface caries), grooved tongue, residual roots, poor restorations and oral cancer, etc. The two most important factors are periodontal disease and thick tongue. Clinically, only 5- 10% of pathological halitosis belongs to non-ostomogenic halitosis. Non-oral halitosis is divided into blood-transported halitosis and non-blood-transported halitosis according to whether the volatile organic compounds need to be transported through the blood to the lungs and expelled through alveolar gas exchange. The main volatile sulfide producing non-oral halitosis is dimethyl sulfide. However, most patients with halitosis are first seen in gastroenterology or otorhinolaryngology in daily outpatient clinics, and most are referred to dentistry only after relevant investigations. This is extremely inconsistent with the fact that only 5-10% of the patients have non-oral halitosis, which means that most of the patients have taken the wrong path. Therefore, the correct order of treatment should start from the oral cavity first, and then be referred to the appropriate specialty by the physician after oral malodor is ruled out. Such a pathway planning is reasonable and can save time and effort and reduce the financial burden. The experience of foreign counterparts supports this approach. Halitosis clinics are also run mainly by periodontists. How to actively scout for the presence or absence of the enemy how to diagnose the degree of having bad breath? At present, there are mainly two types of outpatient clinics, one is the sensory perception analysis method, also known as the nasal test method, which is graded by the examiner’s sense of smell on oral odor, but because the degree of olfactory sensitivity of each examiner varies, so it is difficult to ensure the reliability of the test results if two examiners are chosen at the same time. The other is an objective instrumental test, which analyzes the degree of bad breath by measuring the concentration of sulfide in the patient’s mouth with an electrochemical sensor. This is more objective and reproducible. Of course, how to determine the presence or absence of bad breath without going to the hospital? It can be assessed by the self-perception method (cover the mouth and nose with your hand, exhale through the mouth, and then smell the exhaled gas for yourself to see if there is bad odor) and feedback from people close to you. Can you wash away the bad breath? Oral odor is not the usual easy to cover up body odor, you can not follow the general pattern of covering up, such as mouthwash, chewing gum, etc.. Once the oral odor is detected, the primary treatment is based on the local cause of the oral cavity (periodontal treatment and the correct use of tongue scrapers to clean the tongue, fillings, and correct food embedding). While we pay attention to oral hygiene to prevent the occurrence of oral diseases, we should also improve physical fitness, improve immunity and reduce the reproduction of harmful bacteria; pay attention to nutritional balance in the diet, plus the right amount of aerobic exercise and reasonable and regular rest, so that we can avoid the embarrassment brought by bad breath. Everyone hates the unpleasant smell from the mouth, but if you think about it, how can you pay attention to your health if you are not reminded of the unpleasant smell!