The short answer
Most mouth ulcers are harmless canker sores or come from a bite or irritation, and they heal on their own. A mouth sore, ulcer, or red or white patch that lasts more than two weeks can occasionally be a sign of mouth cancer. See a dentist or doctor to have it checked.
Most mouth ulcers are harmless and heal on their own.
A sore or patch that lasts more than two weeks is worth checking.
Red or white patches or a lump in the mouth are more worth checking.
Risk is higher for people who smoke, chew tobacco, or drink heavily.
Choose how you want to read this
The whole article, with every detail and caution.
This page is for anyone with a mouth sore that is taking a while to heal. It explains the common causes, the signs worth checking, and when to call.
The short answer
Usually not. Canker sores and minor injuries cause most mouth ulcers. MedlinePlus says canker sores are not cancer and can take 1 to 3 weeks to heal fully. NIH's dental research institute says to see a dentist or doctor if a mouth sore, patch or lump lasts more than two weeks. Lasting sores should be checked.
Signs that a mouth sore is worth checking
NIH's dental research institute says to see a dentist or a doctor if a sore, irritation, lump or patch in the mouth lasts more than two weeks. The American Cancer Society says to see a doctor or dentist if these signs last more than a few weeks. This page uses the shorter time. 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
- numbness of the tongue or lip
- loose teeth or pain around the teeth with no dental cause
- a sore throat or a feeling that something is caught in the throat that does not go away
- a lump in the neck
- ear pain
Who is at higher risk
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 (human papillomavirus) infection is also linked to oral cancers. NIH says most throat cancers are caused by HPV. If you use tobacco or drink heavily, mention this clearly when describing a lasting mouth sore.
Far more common causes of mouth sores
Canker sores are painful open sores inside the mouth. MedlinePlus says the pain often goes away in 7 to 10 days, and it can take 1 to 3 weeks for a canker sore to heal completely. Mouth injury, such as biting the tongue or cheek or rough tooth cleaning, can bring one on. Cold sores are caused by the herpes simplex virus and usually appear on or near the lips. MedlinePlus says they go away on their own in 1 to 2 weeks. Most mouth sores fall into one of these categories.
What a doctor checks next
Your dentist or doctor examines the sore's size, color, and texture, and asks how long it has been there. MedlinePlus says your provider can often diagnose a canker sore by looking at it. You may need further testing or a biopsy to look for other causes. MedlinePlus says to contact your provider if a mouth ulcer does not go away after 2 weeks of home care, or gets worse. A biopsy means removing a small piece of tissue to check under a microscope.
What a normal look does not rule out
A visual exam alone cannot always tell an early cancer from a stubborn canker sore. That is why a sore that lasts more than two weeks deserves a closer look. Ask your care team whether a biopsy is needed rather than waiting longer.
When to get help sooner
- 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. Do not drive yourself.
- 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.
- If you are getting chemotherapy, had a stem cell transplant or CAR T therapy, or have low white blood cells, call your care team right away, day or night, if you get a new mouth sore or mouth pain, chills, a sore throat, burning when you pass urine, or any other sign of infection. Do this even if your temperature is normal. The CDC says to call your doctor immediately for a temperature of 100.4°F (38°C) or higher.
- Call your care team or dentist within a day or two if a sore has lasted more than two 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.
What to ask your doctor
- 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?
Sources
Common questions
Does a mouth ulcer mean mouth cancer?
Usually not. Most mouth ulcers are harmless canker sores or come from irritation, and they heal on their own. A sore that lasts more than two weeks is worth checking.
When should a mouth sore be checked?
When it lasts more than two weeks, or there is a red or white patch, a lump, ongoing pain, or numbness.
Who is at higher risk of mouth cancer?
People who smoke, use chewing tobacco, or drink heavily are at higher risk and should get non-healing sores checked.
Can a dentist help?
Yes. Dentists often spot mouth problems early during check-ups, so regular dental visits are useful.
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Sources last checked: 2026-07-12 what this meansLast updated: 2026-09-29Next planned review: 2027-07-12
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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