Oral ulcer can be caused by many reasons, mainly nutrient deficiency (mainly B vitamins) and herpes virus recurrence. Followed by dental diseases and incomplete occlusion and long-term unilateral chewing of food. The rare reasons are ectopic or pathological changes of mandibular joint, deformation of dentures after long-term use or improper manufacture of dentures, oral flat wart and so on. The most rare are oral tumors.
Among all kinds of causes of oral ulcer, only one does not need treatment, that is, the recurrence of herpes virus. The immune system can eliminate herpes virus, just as the immune system can eliminate cold virus and many other viruses. Therefore, oral ulcer caused by herpes virus is a self-limiting disease, and no treatment or medicine is needed. Most people are infected with herpes virus when they are young (some people have symptoms, others have no symptoms). Once they are infected with herpes virus, they will carry the virus for life and can't get rid of it. It will recur when you have other diseases or your immunity is reduced. Generally, the self-healing time is similar to that of a cold, and it takes about a week.
If the oral ulcer doesn't heal itself within two weeks, you should go to the hospital for investigation, find out the cause of the oral ulcer, and then treat the disease to make the oral ulcer heal.