Mouth Sore That Won't Heal: When to See a Dentist

What causes most mouth sores?

The majority of mouth sores are one of a handful of common, benign causes:

• Aphthous ulcers (canker sores) — small, round, shallow sores with a white or yellow center and a red border, usually on the inner cheeks, tongue, or floor of the mouth. They are not contagious and typically resolve within 7–14 days without treatment.
• Trauma — biting the cheek, a sharp food edge, or an ill-fitting denture or orthodontic appliance can cause a sore that mimics a canker sore. These heal within one to two weeks once the source of irritation is removed.
• Herpes simplex (cold sores) — caused by HSV-1, these typically appear on the lips or just outside the mouth, are preceded by tingling, blister, and then crust over within seven to ten days.
• Fungal infection (oral thrush) — white, creamy patches that can be wiped off, often in people who use inhaled steroids, have dry mouth, wear dentures, or have a weakened immune system 1Ref 1National Institute of Dental and Craniofacial Research (2024).Oral Cancer.Warning signs of oral cancer including persistent sores, white or red patches, and numbness; risk factors of tobacco, alcohol, and HPV; and the role of regular dental examination in early detection.

Why does the two- to three-week mark matter?

Normal healing processes — even for larger ulcers or trauma-related sores — are generally complete within two to three weeks. The National Institute of Dental and Craniofacial Research advises seeing a dentist or doctor for any oral symptom that has persisted for more than two weeks 2Ref 2National Institute of Dental and Craniofacial Research (2020).The Oral Cancer Exam.NIDCR guidance to see a dentist or doctor for any oral symptom lasting more than two weeks; the clinical examination and biopsy as the pathway to diagnosis. An oral lesion that has not healed in this window has moved beyond the expected recovery time for a benign cause and warrants professional evaluation.

This does not mean persistence equals cancer. Most sores still turn out to be benign. But because oral cancer is most successfully treated early, the standard clinical recommendation is to evaluate promptly rather than continue watching and waiting.

What makes a mouth sore more concerning?

Certain features raise the priority for evaluation regardless of how long the sore has been present:

• Duration beyond two to three weeks with no sign of healing
• Size that is growing rather than shrinking
• Irregular, raised, or hardened edges
• Red or white patches (erythroplakia or leukoplakia) that cannot be wiped off
• Painlessness — many early oral cancers are not painful, which is why they are sometimes ignored 2Ref 2National Institute of Dental and Craniofacial Research (2020).The Oral Cancer Exam.NIDCR guidance to see a dentist or doctor for any oral symptom lasting more than two weeks; the clinical examination and biopsy as the pathway to diagnosis
• Numbness or tingling in the tongue, lip, or jaw area
• Difficulty chewing, swallowing, or moving the tongue
• A lump in the neck alongside a mouth sore
• History of tobacco or alcohol use, or prior HPV infection — all established risk factors for oral cancer 1Ref 1National Institute of Dental and Craniofacial Research (2024).Oral Cancer.Warning signs of oral cancer including persistent sores, white or red patches, and numbness; risk factors of tobacco, alcohol, and HPV; and the role of regular dental examination in early detection

If any of these features are present, see a dentist or physician promptly rather than waiting a full three weeks.

What will a dentist or doctor do?

At an evaluation, the clinician will take a history (how long, any pain, tobacco or alcohol use, recent trauma) and examine the sore closely, feeling the edges and checking lymph nodes in the neck.

For a sore that looks clearly benign and has an identifiable cause (such as a sharp denture clasp), the dentist may fix the source and ask you to return in one to two weeks to confirm healing.

For any sore that looks suspicious or fails to heal after the source of irritation is removed, the next step is usually a biopsy — a small tissue sample sent to a pathology laboratory. This is the only definitive way to distinguish a benign sore from precancerous or cancerous tissue 2Ref 2National Institute of Dental and Craniofacial Research (2020).The Oral Cancer Exam.NIDCR guidance to see a dentist or doctor for any oral symptom lasting more than two weeks; the clinical examination and biopsy as the pathway to diagnosis. The procedure is typically done in the dental or oral surgery office under local anesthesia.

Why early detection matters: what the data shows

Data from the American Cancer Society on cases diagnosed between 2015 and 2021 show that the five-year relative survival rate for oral cavity cancers detected at the localized stage — before spreading to lymph nodes or distant structures — ranges from roughly 72 to 95 percent depending on the specific site 3Ref 3American Cancer Society (2024).Survival Rates for Oral Cavity and Oropharyngeal Cancer.Five-year relative survival rates for oral cavity cancers by stage (localized vs. regional vs. distant), supporting the importance of early evaluation for non-healing sores. Once disease has spread to regional lymph nodes, survival rates drop substantially. For oropharyngeal cancers detected at a localized stage the five-year rate is approximately 86 percent 3Ref 3American Cancer Society (2024).Survival Rates for Oral Cavity and Oropharyngeal Cancer.Five-year relative survival rates for oral cavity cancers by stage (localized vs. regional vs. distant), supporting the importance of early evaluation for non-healing sores.

This difference in outcomes is the practical reason behind prompt evaluation of a non-healing sore: an early biopsy, if positive, changes the prognosis considerably compared with a delayed diagnosis.

What can you do while waiting for your appointment?

While waiting for an evaluation:

• Remove any obvious source of irritation — if a broken tooth or sharp denture edge contacts the sore, use a small piece of dental wax over the sharp edge for protection.
• Avoid tobacco and alcohol, both of which delay healing and are independent risk factors for oral cancer 1Ref 1National Institute of Dental and Craniofacial Research (2024).Oral Cancer.Warning signs of oral cancer including persistent sores, white or red patches, and numbness; risk factors of tobacco, alcohol, and HPV; and the role of regular dental examination in early detection.
• Rinse gently with saltwater (half a teaspoon of salt in a cup of warm water) to keep the area clean — this may offer some comfort but does not treat the underlying cause.
• Avoid very spicy, acidic, or rough-textured foods that can irritate the sore further.

Do not apply topical pain relievers directly to an unevaluated sore — they may mask symptoms that help a clinician characterize the lesion.

Who should you see?

A dentist is usually the right first contact for a mouth sore — they see oral lesions regularly and are trained to distinguish common sores from those requiring further work-up. If you don't have a dentist, a primary care physician can do an initial evaluation and refer appropriately.

If a biopsy suggests a precancerous or cancerous lesion, referral to an oral and maxillofacial surgeon or an otolaryngologist (ENT) with head and neck oncology experience follows. The NIDCR offers a guide to finding low-cost dental care through dental schools, community health centers, and federally funded clinics for those without a regular dentist 4Ref 4National Institute of Dental and Craniofacial Research (2024).Finding Dental Care.Options for low-cost dental care including dental schools, community health centers, Medicaid, and federally funded clinics for patients who lack access to a regular dentist.

Gale can help you find a dentist, prepare questions for your appointment, and connect you with a primary care clinician who can coordinate specialist referrals.