Canker sores (mouth ulcers): causes, how they heal and when to see a dentist

What is a canker sore, and how does it differ from a cold sore?

A canker sore (recurrent aphthous stomatitis) is a superficial ulcer inside the mouth — cheek, inner lip, edge of the tongue, under the tongue. It is not contagious and not caused by a virus. A cold sore, by contrast, is caused by the herpes virus, usually appears as clustered blisters on the outside of the lip or on firm tissue such as the gum, and is contagious. The distinction changes the treatment.

Types

• Minor: The commonest (80 %). 2–8 mm, heals without scarring in 7–14 days.
• Major: Larger than 1 cm, deep, can last 2–6 weeks and may scar.
• Herpetiform: Many pinhead-sized ulcers in clusters; confused with cold sores but not viral.

Triggers

• Mechanical trauma such as biting the cheek or lip, a hard brush, an overhanging filling or a wire
• Stress, lack of sleep, hormonal phases (premenstrual)
• Toothpastes containing sodium lauryl sulphate (SLS)
• Deficiency of iron, B12, folate, zinc
• Acidic and spicy foods, chocolate, nuts, strawberries, tomatoes (varies by person)
• The period after stopping smoking (a temporary increase)
• Some medicines (NSAIDs, beta blockers)

What can you do at home?

1. Rinse several times a day with warm salt water or bicarbonate water
2. Avoid acidic, hot and spicy foods; choose soft, cool foods
3. Switch to an SLS-free toothpaste and a soft brush
4. A protective gel/paste or a local-anaesthetic gel from the pharmacy applied to the ulcer (short term)
5. Antiseptic mouthwash (chlorhexidine) — limited to 1–2 weeks, may stain the teeth

Rubbing painkillers on, placing aspirin on the ulcer, or "burning" it with alcohol or lemon delays healing.

In the clinic

The dentist identifies the type of ulcer; corrects any source of trauma (a sharp tooth edge, an overhanging filling, a wire end); may prescribe a short course of a corticosteroid paste or rinse for large or very painful ulcers; and in frequently recurring cases requests blood tests (iron, B12, folate, zinc, full blood count) and, if needed, assesses jointly with a physician or dermatologist.

When to see a professional

• An ulcer not healed in 2 weeks — other causes, including oral cancer, must be excluded
• Ulcers larger than 1 cm, many at once, or recurring more than 6 times a year
• With fever, malaise, eye or skin findings, or genital ulcers (systemic causes such as Behçet's disease are investigated)
• Pain that prevents eating and drinking, especially in children

Reducing recurrences

Keep a trigger-food diary, use SLS-free toothpaste, sleep regularly, manage stress, replace deficient vitamins and minerals on medical advice, and have sharp tooth or filling edges smoothed. Checking the gums and oral mucosa is part of the routine examination; oral lesions are also assessed at 6-monthly check-ups.