According to the World Health Organization (WHO), the number of people who die from smoking-related diseases worldwide is now as high as 10 million per year, and smoking has become one of the most serious public problems in the world today, as well as the biggest problem facing human health. The oral cavity is the gateway to the human body, the harm of smoking, the first to bear the brunt. Smoking can not only cause bad breath, periodontal disease, or oral cancer and oral mucosal disease is an important cause, seriously affecting oral health and daily life. Oral cancer accounts for 5%-6% of the total body tumors, and is one of the 6 most common cancers in the world. 2005 Third National Oral Health Survey shows that oral cancer and precancerous lesions in the age group of 35-44 years old is 17/100,000, and in the age group of 65-74 years old is 27/100,000, and a lot of epidemiological researches have confirmed that oral cancer and precancerous lesions are the most common cancers in the world. A large number of epidemiologic studies have confirmed that smoking is closely related to oral cancer, and the incidence and mortality rate of oral cancer among smokers is 2-3 times higher than that of non-smokers. In addition, smoking can aggravate the risk of recurrence of oral cancer. 40% of the smokers who continue to smoke after the cure of oral cancer can develop second primary cancer, while only 6% of the smokers who quit smoking after the cure, and the 5-year survival rate of non-smokers after the treatment is significantly higher than that of the smokers. The occurrence of oral cancer is directly proportional to the duration and amount of smoking. There are also studies confirming that smoking and drinking have synergistic effect on the occurrence of oral cancer. If there is smoking and drinking habit, the effect of smoking and drinking will increase the risk of oral cancer by 2.5 times. Halitosis is the bad odor emitted from the mouth when breathing, which is one of the reasons affecting people’s social interaction and causing psychological disorders. Oral microbial corruption and digestion of oral stagnant substances produce volatile sulfide and other odor substances is the main component of bad breath. Some studies have confirmed that smoking can make the oral cavity volatile sulfide content significantly higher. Cigarette smoke contains a large number of volatile sulfides, and a large number of smoking can form a hairy tongue so that food residue retention, saliva secretion is reduced and exacerbated halitosis. Periodontal disease is one of the most common infectious diseases in humans. The third national oral health epidemiologic survey shows that the periodontal health rate of 35-44 age group is 14.2%, and the periodontal health rate of 65-77 age group is 13.6%. The occurrence of periodontal disease can not only be manifested as bleeding gums, periodontal pocket formation, alveolar bone resorption, but also lead to loosening and loss of teeth, seriously affecting daily life. Smoking is one of the recognized risk factors for periodontal disease. Many studies have proved that there is a close relationship between smoking and the occurrence and development of periodontal disease. The prevalence of periodontal disease is higher and more severe in smokers than in non-smokers, and the longer the age of smokers and the more cigarettes they smoke per day, the more severe the periodontal disease. Oral mucosal leukoplakia Smoking is the direct causative factor of oral mucosal leukoplakia. Long-term smoking, the harmful substances in tobacco can stimulate the oral mucosa, direct attack on the oral mucosa epithelial cells, so that it changes, smoking high temperature is the oral mucosa contact part of the burn. Epidemiologic investigation shows that the risk of smokers suffering from leukoplakia is significantly higher than that of non-smokers, and the longer the age of smokers and the more they smoke every day, the higher the risk of leukoplakia of oral mucosa.