The harm of smoking to human health should be very clear to everyone, but the harm of smoking to the oral cavity have you ever noticed? Many people think that the impact of smoking on the oral cavity is at most yellow teeth and black teeth, in fact, the harm of smoking on the oral cavity is much more than that, a variety of oral diseases are caused by smoking, and can even cause oral cancer. What are the hazards of smoking to the oral cavity, let’s take a look: 1, oral cancer oral cancer accounts for 5%-6% of the whole body tumors, is one of the six most common cancers in the world. A large number of epidemiological studies have confirmed that smoking and oral cancer are closely related, 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 increase the risk of developing oral cancer again. For those who continue to smoke after curing oral cancer, 40% of them will develop the second primary cancer, while only 6% of those who quit smoking after curing; the survival rate of non-smokers is significantly higher than that of smokers within 5 years after treatment. The occurrence of oral cancer is directly proportional to the duration of smoking and the amount of smoking. There are also studies that show that smoking and alcohol consumption have a synergistic effect on the occurrence of oral cancer. If there is a habit of smoking and alcohol consumption, coupled with the effect of alcohol consumption, the risk of oral cancer will increase by 2.5 times. 2.Bad breath is the bad smell from the mouth when breathing, which is one of the reasons that affect people’s social interaction and cause psychological disorders. Microorganisms in the oral cavity to digest the substances retained in the mouth to make it corrupt, producing volatile sulfide and other odors is the main component of halitosis. Some studies have confirmed that smoking can significantly increase the level of volatile sulfides in the mouth. Smoke contains a large number of volatile sulfides, while a large number of smoking may also form a hairy tongue caused by the retention of food residues, saliva secretion is reduced and intensify bad breath. 3, periodontal disease periodontal disease is one of the most common infectious diseases in humans. The third national oral health epidemiological survey shows that the periodontal health rate for the age group of 35-44 years old is 14.2%, and the periodontal health rate for the age group of 65-77 years old is 13.6%. The occurrence of periodontal disease is not only manifested by gum bleeding, periodontal pocket formation, alveolar bone resorption, but also can lead to loosening and loss of teeth, which seriously affects daily life. Smoking is one of the recognized high-risk factors for periodontal disease. Many studies have demonstrated a close relationship between smoking and the generation and development of periodontal disease. Smokers have a higher prevalence of periodontal disease than non-smokers, the disease is more serious, and the longer the smoking age, the more the amount of smoking per day, the more serious periodontal disease. 4, oral mucosa white spots smoking is a direct causative factor of oral mucosa white spots. Long-term smoking, the harmful substances in tobacco will stimulate the oral mucosa, directly attack the oral mucosa epithelial cells, so that they change, and smoking, high temperature but the oral mucosa contact part of the burn. Epidemiological survey shows that smokers are significantly more likely to suffer from leukoplakia than non-smokers, and the longer the smoking age and the more the daily smoking amount, the higher the risk of oral mucosal leukoplakia.