Aphthous ulcers — commonly known as canker sores — are small, painful sores that develop on the soft tissues inside the mouth. They are the most common type of oral ulceration, affecting up to 20% of the general population. Unlike cold sores, canker sores are not caused by a virus and are not contagious. Most heal on their own within one to two weeks, though treatment can help manage pain and speed recovery.
What Are Aphthous Ulcers?
Aphthous ulcers are recurrent, shallow lesions that form on the non-keratinized (soft, moveable) mucous membranes of the mouth — the inside of the lips, cheeks, floor of the mouth, soft palate, and the underside of the tongue. They do not occur on the hard palate, attached gingiva, or the outer lip surface (which distinguishes them from cold sores).
There are three clinical types:
- Minor aphthous ulcers — The most common (80% of cases). Small (less than 10mm), oval, with a yellowish-white center and red border. Heal within 7-14 days without scarring.
- Major aphthous ulcers — Larger (over 10mm), deeper, and more painful. May take 2-6 weeks to heal and can leave scars.
- Herpetiform ulcers — Multiple tiny (1-3mm) ulcers that may cluster together. Despite the name, they are not caused by herpes virus.
Aphthous ulcers affect approximately 20% of the general population, with some studies reporting higher rates among young adults and women (Journal of Oral Pathology & Medicine, 2018).
Causes and Risk Factors
The exact cause of aphthous ulcers is not fully understood. They appear to result from a combination of genetic, immunological, and environmental factors. Common triggers include:
- Minor oral trauma — Biting the cheek, aggressive toothbrushing, dental work, or rough foods
- Stress — Emotional or physical stress is one of the most commonly reported triggers
- Nutritional deficiencies — Iron, vitamin B12, folate, and zinc deficiencies are associated with increased occurrence
- Sodium lauryl sulfate (SLS) — This foaming agent in many toothpastes may irritate the mucosa and trigger ulcers in susceptible individuals
- Hormonal changes — Some women report ulcers associated with menstrual cycles
- Food sensitivities — Citrus fruits, tomatoes, chocolate, coffee, nuts, and cheese are common triggers for some people
- Immune system factors — Aphthous ulcers are thought to involve a T-cell-mediated immune response
- Family history — A genetic predisposition is suggested by the fact that aphthous ulcers often run in families
- Underlying conditions — Celiac disease, inflammatory bowel disease (Crohn's, ulcerative colitis), and Behcet's disease are associated with recurrent aphthous ulcers
Symptoms
The typical presentation of an aphthous ulcer includes:
- A tingling or burning sensation 1-2 days before the ulcer appears
- A round or oval sore with a white or yellowish center and a red, inflamed border
- Pain, especially when eating, drinking, or speaking
- Tenderness in the surrounding tissue
- In minor ulcers: one to five sores at a time
- In severe cases: difficulty eating or drinking due to pain
Aphthous ulcers should not be confused with cold sores (herpes simplex virus), which typically appear on the outer lip and are preceded by a tingling or itching sensation. If you have sores that occur on the attached gums, hard palate, or outer lips, consult your dentist for proper diagnosis.
Treatment and Prevention
Most minor aphthous ulcers heal spontaneously within one to two weeks. Treatment aims to reduce pain, speed healing, and prevent recurrence.
Topical treatments:
- Topical corticosteroids — Triamcinolone dental paste or fluocinonide gel applied directly to the ulcer to reduce inflammation
- Topical anesthetics — Benzocaine gel or lidocaine rinse to numb pain before eating
- Antiseptic rinses — Chlorhexidine mouthwash may reduce duration and pain
- Protective pastes — Over-the-counter products that coat the ulcer and shield it from irritation
Systemic treatments (for severe or frequently recurring ulcers):
- Colchicine, dapsone, or systemic corticosteroids in refractory cases
- Treatment of underlying nutritional deficiencies (iron, B12, folate supplementation)
- Evaluation for celiac disease or inflammatory bowel disease if ulcers are recurrent and severe
Prevention and self-care:
- Switch to an SLS-free toothpaste if SLS appears to be a trigger
- Avoid known food triggers
- Use a soft-bristled toothbrush and gentle brushing technique
- Manage stress through relaxation techniques, exercise, or counseling
- Ensure adequate intake of iron, B12, folate, and zinc
- Protect the mouth from accidental biting by eating slowly and carefully
Research in Cochrane Database of Systematic Reviews (2019) supports topical corticosteroids as the most evidence-based treatment for reducing pain and healing time of aphthous ulcers.
If you experience frequent, large, or unusually persistent mouth sores, consult your dentist or physician to rule out underlying conditions and discuss a management plan.