There are many reasons for the frequent appearance of ulcers in the mouth, which are the clinical manifestations of many diseases, the most common being Aphthous ulcer, Leukoarthrosis, traumatic ulcers, oral mucosal damage of herpetic skin diseases such as aspergillosis, which can have erosions or even ulcers. Drug allergy can appear oral ulcers, and some connective tissue diseases such as systemic lupus erythematosus can have oral ulcers, cancerous ulcers and so on. Therefore, there are many diseases that cause mouth ulcers, so it is recommended that patients should go to a regular hospital, ask the doctor to clarify what causes or diseases cause mouth ulcers, and give reasonable treatment to remove the causes to avoid recurrence of ulcers.