Is a Mouth Ulcer a Sign of Mouth Cancer?

Usually not. Canker sores and minor injuries cause most mouth ulcers, and they heal within one to two weeks. A sore that does not heal after a few weeks can be a sign of mouth cancer, so lasting sores should be checked.

The American Cancer Society advises seeing a doctor or dentist if a mouth sore lasts more than a few weeks. Other symptoms to mention include a white or red patch on the gums, tongue, or the lining of the mouth, a lump or thickened area in the lips, mouth, or cheek, and numbness of the tongue or lip. Loose teeth or pain around the teeth with no dental cause, and ear pain, are also worth mentioning.

Tobacco use, including smoking and smokeless tobacco, is one of the strongest risk factors for mouth cancer. Heavy alcohol use raises the risk too, and the two together raise it more than either alone. HPV, a common virus, is linked to a growing number of throat and mouth cancers, including in people who have never smoked. If you use tobacco or drink heavily, mention this clearly when describing a lasting mouth sore.

Canker sores are small, painful ulcers inside the mouth that are not contagious and usually heal within one to two weeks on their own. Cold sores, caused by a virus, typically appear on or near the lips and also heal within about two weeks. Biting your cheek or tongue, a rough tooth or denture, and braces can all cause a sore that heals once the irritation stops. Most mouth sores fall into one of these categories.

Your dentist or doctor examines the sore's size, color, and texture, and asks how long it has been there. If the sore looks like a typical canker sore or an irritation from a rough tooth, removing the irritant and watching for two to three weeks is often reasonable. If the sore has lasted more than a few weeks despite this, or looks unusual, a biopsy is the next step: removing a small piece of tissue, often under local numbing, to check under a microscope. Results are typically ready within about a week.

A visual exam alone cannot always tell an early cancer from a stubborn canker sore, which is why any sore that outlasts the usual healing window deserves a biopsy rather than more waiting.

• Call 911 or go to an emergency department if swelling in the mouth, floor of the mouth, jaw or neck makes breathing or swallowing hard, pushes your tongue up, or comes with a fever and a fast heartbeat. Mouth infections can close an airway within hours.
• Call your care team or dentist the same day if the sore bleeds when nothing has touched it. Do the same if swelling in your mouth, jaw or face is spreading. Do the same if it now hurts too much to eat or open your mouth.
• Call your care team or dentist within a day or two if a sore has sat there for three to four weeks and has not healed. Call too if it is growing. Call if you also see a white or red patch, or feel a thick area in the lip or cheek. A numb tongue or lip, ear pain, or teeth that loosen for no dental reason all count.

• This sore has not healed in [how long] — should it be biopsied?
• Could this be a canker sore, cold sore, or irritation from a tooth?
• Am I at higher risk given my tobacco or alcohol use?
• How should I watch it if we decide to wait?

• American Cancer Society — Signs and Symptoms of Oral Cavity and Oropharyngeal Cancer
• CDC — Basic Information About HPV and Cancer