There are many causes of oral ulcers, they recur easily, and heal slowly. Frequent ulcers make many people worry about the possibility of cancerous changes. If an oral ulcer does not heal over a long period, there indeed is a tendency for it to turn cancerous. Chronic ulcers are also a cause of cancer, so it is essential to pay attention to one's oral health. For instance, oral ulcers must be treated promptly to eliminate the cause and provide symptomatic treatment. Treatment methods should combine systemic and local treatments. It is especially important to pay attention to those oral ulcers that do not heal over an extended period, as they are precancerous lesions and are very likely to turn cancerous. A biopsy may be necessary to make a definitive diagnosis to facilitate timely treatment.