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

Mouth ulcers are incredibly common. Most adults will experience them at some point. They are usually harmless, painful for a few days, and heal on their own within one to two weeks. But what happens when a mouth ulcer does not go away? While it is easy to dismiss a persistent sore as "just an ulcer," there are times when a non-healing ulcer requires urgent professional assessment.

Common Causes of Mouth Ulcers

Most mouth ulcers are aphthous ulcers -- small, round or oval sores with a white or yellowish centre and a red border. They are not contagious and, while the exact cause is not fully understood, several triggers have been identified:

• Trauma: Biting the inside of your cheek, sharp edges on teeth or fillings, vigorous brushing, or irritation from orthodontic braces are among the most common triggers
• Stress and fatigue: Many people notice ulcers appearing during periods of heightened stress or when they are run down
• Vitamin and mineral deficiencies: Low levels of iron, vitamin B12, or folate can make you more susceptible to recurring ulcers
• Hormonal changes: Some women find they are more prone to ulcers at certain points in their menstrual cycle
• Certain foods: Acidic fruits (citrus, tomatoes), chocolate, coffee, and spicy foods may trigger ulcers in susceptible individuals
• Sodium lauryl sulphate (SLS): This foaming agent found in many toothpastes has been linked to ulcer recurrence in some people. Switching to an SLS-free toothpaste may help

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Types of Mouth Ulcers

Minor Aphthous Ulcers

These are the most common type, accounting for around 80% of all mouth ulcers. They are typically small (less than 10mm), round or oval, and heal within 10-14 days without scarring. You may get one or a few at a time. They are painful but manageable.

Major Aphthous Ulcers

Less common but significantly more troublesome, major ulcers are larger (over 10mm), deeper, and can take several weeks or even months to heal. They may leave scarring and can be extremely painful, sometimes making eating and drinking difficult. Major ulcers should always be assessed by a dentist.

Herpetiform Ulcers

Despite the name, herpetiform ulcers are not caused by the herpes virus. They appear as clusters of many tiny (1-2mm) ulcers that can merge together to form larger, irregular sores. They are uncommon and tend to affect women more than men. They usually heal within two weeks but can be very painful.

Home Remedies and Self-Care

For typical minor ulcers, several approaches can help manage pain and promote healing:

• Salt water rinse: Dissolve half a teaspoon of salt in a glass of warm water and rinse gently. This can help keep the area clean and may reduce inflammation. Repeat after meals.
• Benzydamine spray or mouthwash: Available over the counter from UK pharmacies (brand name Difflam), benzydamine provides local pain relief and has anti-inflammatory properties. It can be particularly helpful before eating.
• Topical gels and pastes: Antimicrobial gels (such as those containing chlorhexidine) or protective pastes can coat the ulcer, shielding it from irritation and helping it heal.
• Avoid trigger foods: Steer clear of acidic, spicy, or sharp foods (like crisps and crusty bread) that can irritate the sore.
• Use a soft-bristle toothbrush: This reduces the risk of traumatising the ulcer or surrounding tissue during brushing.
• Try an SLS-free toothpaste: If you get frequent ulcers, switching to a toothpaste without sodium lauryl sulphate may reduce recurrence.

When to Worry: Red Flags

While the vast majority of mouth ulcers are benign, certain features should prompt you to seek professional assessment without delay:

• An ulcer lasting more than three weeks -- this is the most important red flag
• A painless ulcer -- most benign ulcers are painful; a painless sore may be more concerning
• An ulcer that is growing rather than shrinking
• Unexplained lumps or swellings in the mouth or neck
• Red or white patches on the lining of the mouth, tongue, or gums that do not rub off
• Unexplained numbness in the tongue, lip, or cheek
• Persistent difficulty swallowing or a feeling of something stuck in the throat
• Unexplained loose teeth -- see our article on loose teeth in adults

Mouth Cancer Awareness

Mouth cancer (oral cancer) affects over 8,800 people in the UK each year, according to Cancer Research UK. The incidence has been rising over the past two decades. Risk factors include smoking, heavy alcohol consumption, HPV infection, and excessive sun exposure (for lip cancer). However, around a quarter of mouth cancer cases occur in people with no obvious risk factors.

The most important thing to understand about mouth cancer is that early detection dramatically improves outcomes. When mouth cancer is diagnosed early, survival rates are significantly higher. This is why the three-week rule exists -- it serves as a simple, memorable prompt for both patients and clinicians to investigate non-healing ulcers.

Your dentist checks for signs of mouth cancer as part of a routine dental examination. This is one of the many reasons regular dental check-ups are so important, even if your teeth feel fine. If your dentist spots anything concerning, they can refer you for further investigation under the NHS urgent suspected cancer pathway, which aims to see patients within two weeks.

When Recurring Ulcers Suggest an Underlying Condition

If you experience frequent mouth ulcers (more than three or four episodes per year), it may be worth investigating potential underlying causes with your GP. Conditions that can present with recurring oral ulceration include:

• Iron, B12, or folate deficiency -- a simple blood test can check for this
• Coeliac disease -- an autoimmune reaction to gluten that can cause mouth ulcers alongside other symptoms
• Crohn's disease and other inflammatory bowel conditions
• Immune deficiency or immunosuppression
• Behcet's disease -- a rare condition causing recurring ulcers in the mouth and other areas