Mouth ulcers that need to be alerted to cancer are malignant mouth ulcers, chronic traumatic mouth ulcers, and tongue ulcers that do not heal for a long time. 1. Malignant mouth ulcers Benign mouth ulcers can heal in a few weeks or days, while malignant mouth ulcers do not heal for a long time. Malignant mouth ulcers are not clearly demarcated from the surrounding tissues, with uneven boundaries, uneven bases, and weaker pain than benign ulcers. 2. Chronic traumatic oral ulcers There are residual roots and crowns and sharp tooth tips in patients, and their sharp edges constantly stimulate and scrape the tongue and buccal mucosa, which is easy to develop into chronic oral ulcers, and if the stimulating factors are not removed, it is easy to develop into tongue cancer or buccal cancer. 3. Tongue ulcers that do not heal for a long time The degree of malignancy of active organs is higher, which can directly lead to the impaired movement of tongue, and in serious cases, it affects speech and eating. If mouth ulcers do not heal for a long time, you should consult doctor in time to avoid delaying the treatment.