Oral submucous fibrosis (OSF) is a chronic disease that can invade any part of the oral cavity. Due to the degeneration of fibrous tissue and epithelial atrophy in the lamina propria, it causes mucosal sclerosis and the formation of striae, which eventually causes dental closure and hinders the performance of various oral functions and becomes a precancerous state. Four signs to check whether oral mucosa fibrosis is cancerous 1. Ulcers do not heal: the duration of oral ulcers usually does not exceed two weeks, if symptoms such as burning sensation and pain do not heal for more than two weeks, it is necessary to be alert to the possibility of oral cancer. Because, oral cancer is often manifested in the form of ulcers with elevated edges around and uneven center, covered with necrotic tissue and obvious pain. One of the important reasons why oral cancer is difficult to detect is that most oral cancers are painless in the early stage. 2.Obvious pain: Early stage is generally painless or only has local abnormal rubbing sensation, and pain is obvious after ulceration. With further invasion of nerve by tumor, it can trigger ear and throat pain. 3.Lymph node enlargement: Oral cancer mostly metastasizes to nearby lymph nodes in the neck. Sometimes the primary lesion is small and even the symptoms are not obvious yet, but metastatic cancer cells are found in the lymph nodes in the neck. Therefore, if the lymph nodes in the neck are suddenly enlarged, the oral cavity needs to be examined. 4.Dysfunction: The tumor may invade the muscles of opening and closing the mouth and the jaw joint, resulting in limited movement of opening and closing the mouth. It should be emphasized that although the above symptoms are common symptoms of oral cancer, they are not completely used to determine whether one has cancer or not. Because the above symptoms may also appear in oral inflammation, it is better to go to hospital for timely consultation, early and clear diagnosis and symptomatic treatment.