It is recommended to quit smoking when mouth ulcers appear. Harmful substances produced by smoking and the temperature stimulation of tobacco combustion may affect the normal healing of mouth ulcers and even lead to other oral mucosal diseases, as follows. 1. Harmful substances produced by smoking: such as dimethylbenzanthracene has an irritating effect on the oral mucosa, acrolein and cyanide will reduce the respiration of the epithelial cells of the oral mucosa, inhibit the formation of RNA, and make the mucosal keratinization process abnormal. 2. Tobacco burning temperature stimulation: long-term temperature stimulation will lead to oral ulcers can not heal normally, or epithelial hyperplasia, accompanied by excessive positive keratinization or excessive incomplete keratinization. If the mouth ulcers have not healed for a long time, or other symptoms appear, it is recommended to go to the hospital in time to receive professional treatment as soon as possible.