A mouth ulcer is an ulcerative disease that occurs on the mucous membrane of the oral cavity and may form when the body’s immunity is low during a fire. The cause of mouth ulcers is low resistance. When the body’s immunity is low, there may be vitamin deficiency or weak response to local stimulation and weak protection of the body, and local ulcers may be formed; it is also easy to make bacterial and viral infection, and then ulcers are formed. Once the oral ulcer is formed, it will form a very obvious clinical manifestation of redness, yellowness, concavity and pain on the mucosal surface. You can spray topical open-throat sword spray or ulcer powder, watermelon cream, Yunnan Baiyao, etc. to promote the healing of the ulcer surface. Patients with severe pain can also be treated by applying local anesthetic drugs. Mouth ulcers are self-healing in nature and will heal on their own in about 2 weeks.