1.Long-term addiction to smoking and alcohol Most oral cancer patients have a long-term history of smoking and drinking, while oral cancer is rare in non-smokers and non-drinkers. 2.Poor oral hygiene Poor oral hygiene creates conditions for bacteria or mold to breed and multiply in the oral cavity, which is conducive to the formation of nitrosamines and their precursors. Coupled with stomatitis, some cells are in a proliferative state and more sensitive to carcinogens, so all these reasons may promote the occurrence of oral cancer. 3.Long-term stimulation of foreign body Dental roots or sharp tooth tips, unsuitable dentures stimulate oral mucosa for a long time, resulting in chronic ulcers and even cancer. 4.Malnutrition Vitamin A deficiency can cause epithelial thickening and hyperkeratosis of oral mucosa, which is related to the occurrence of oral cancer. Demographic studies show that countries with low intake of vitamin A have high incidence of oral cancer. It is also thought to be related to insufficient intake of micronutrients, such as low zinc content in food. Zinc is an indispensable element for the growth of animal tissues, and zinc deficiency may lead to mucosal epithelial damage, creating favorable conditions for the development of oral cancer. In addition, insufficient intake of total protein and animal protein may be related to oral cancer. 5.White spots and erythema of mucous membrane White spots and hyperplastic erythema of oral mucous membrane are often a kind of precancerous lesions.