Canker sores, also called aphthous ulcers, are small, shallow, painful sores that develop inside the mouth: on the inner cheeks and lips, the tongue, the gums, or the soft palate. They are not contagious and not caused by a virus, unlike cold sores. Most heal by themselves within a week or two, but they can make eating and talking miserable in the meantime. Here is how to ease the pain and speed healing.
This article is for general information and is not medical advice. See a doctor if symptoms are severe, spreading, affecting your vision, or not improving after a week or two.
What a canker sore looks like
A typical canker sore is round or oval, with a white or yellowish center and a red border, usually 2 to 8mm across. You often feel a tingling or burning spot a day before it appears. Most people get the small (minor) type that heals without scarring. Larger sores and clusters of tiny ones are less common and take longer.
Rinses that help
Salt water
Dissolve half a teaspoon of salt in a cup of warm water and swish for 15 to 30 seconds, then spit. Do this three or four times a day. It is mildly antiseptic and helps clean the area.
Baking soda rinse
One teaspoon of baking soda in half a cup of warm water neutralises acid and reduces irritation. Use it the same way as the salt rinse.
Pharmacy mouthwashes
Antimicrobial rinses containing chlorhexidine, or ulcer-specific rinses with an anaesthetic or anti-inflammatory, can reduce pain and lower the chance of secondary infection. A pharmacist can point you to the right one.
Topical treatments
- Numbing gels with benzocaine or lidocaine give short-term pain relief, useful before meals.
- Protective pastes form a barrier over the sore so food and teeth stop irritating it.
- Corticosteroid pastes (some available over the counter, stronger ones by prescription) reduce inflammation and can shorten healing time if used early.
- Alum or a dab of milk of magnesia are traditional home remedies that some people find soothing.
Foods to avoid while it heals
Acidic foods (citrus, tomatoes, pineapple, vinegar), salty snacks, spicy dishes, and crunchy or sharp foods like crisps and toast will all sting and can slow healing. Stick to soft, bland, cool foods: yoghurt, smoothies, oatmeal, mashed potato. Drink through a straw if a sore is near the front of your mouth.
Reducing how often you get them
- Switch to a toothpaste without sodium lauryl sulfate (SLS), which triggers ulcers in some people.
- Use a soft-bristled toothbrush and brush gently to avoid nicking the lining of your mouth.
- Manage stress and protect your sleep, both strong triggers.
- If you get them constantly, ask your doctor to check iron, B12, folate and zinc levels.
- Note which foods precede a flare and cut back on those.
Related reading
Canker sores are sometimes confused with other mouth and lip issues. If your problem is dry, cracked skin at the corners of the mouth or on the lips rather than inside, see our guides to preventing chapped lips and treating irritation. And if painful skin cracks are an issue elsewhere, such as your feet, our guide on treating cracked heels covers the same principle of protecting a healing wound from repeated stress.
When to get it checked
See a dentist or doctor if a sore lasts more than three weeks, is very large, recurs frequently, is accompanied by fever or fatigue, or if you have never had one before and are over 40. Persistent, non-healing mouth ulcers should always be examined.
Frequently Asked Questions
What is the fastest way to get rid of a canker sore?
Rinse with warm salt water or a baking soda rinse several times a day, apply an over-the-counter benzocaine gel or a protective paste to numb and shield it, and avoid acidic, salty, spicy and crunchy foods. Most small canker sores heal in 7 to 10 days; these steps mainly reduce pain and prevent irritation while they do.
What is the difference between a canker sore and a cold sore?
A canker sore is inside the mouth (inner cheek, tongue, gums, soft palate), is not contagious, and is not caused by a virus. A cold sore appears on or around the lips, is caused by the herpes simplex virus, and is contagious. Treatments are completely different.
What deficiencies cause canker sores?
Recurrent canker sores are linked in some people to low iron, vitamin B12, folate, or zinc. If you get them often, ask your doctor about a blood test. Coeliac disease and inflammatory bowel disease can also cause frequent mouth ulcers.
Why do I keep getting canker sores?
Common triggers include minor mouth injuries (biting your cheek, hard toothbrushing, braces), stress and poor sleep, hormonal shifts, acidic or spicy foods, toothpaste containing sodium lauryl sulfate, and nutritional deficiencies. Keeping a trigger diary often reveals a pattern.
When should I see a doctor or dentist about a canker sore?
Seek advice if a sore is unusually large, lasts longer than three weeks, keeps recurring, spreads to the lips, makes it hard to eat or drink, or comes with a fever. Any mouth ulcer that does not heal after three weeks should be checked to rule out other causes.