Canker sores (mouth ulcers): causes, treatment and how long they last

The NHS says mouth ulcers need time to heal and there is no quick fix. Avoiding things that irritate the ulcer should help speed up healing, reduce pain and reduce the chance of it returning. It suggests using a soft-bristled toothbrush, drinking cool drinks through a straw, eating softer foods, having regular dental check-ups and eating a healthy balanced diet.

It advises not eating very spicy, salty or acidic food, rough or crunchy food such as toast or crisps, very hot or acidic drinks such as fruit juice, and not using toothpaste containing sodium lauryl sulphate.

A pharmacist can recommend a treatment to speed up healing, prevent infection or reduce pain: an antimicrobial mouthwash, a painkilling tablet, mouthwash, gel or spray, corticosteroid lozenges, or a salt (saline) mouthwash. To make a salt mouthwash, dissolve half a teaspoon of salt in a glass of warm water, rinse your mouth and spit it out, and repeat as often as you like. A GP or dentist may prescribe stronger medicine for severe, persistent or infected ulcers, such as steroid sprays or tablets, painkilling gels or mouthwashes to kill germs.

The NHS says most single mouth ulcers are caused by things you can try to avoid: biting the inside of your cheek, badly fitting dentures, braces, rough fillings or a sharp tooth, cuts or burns while eating or drinking, a food intolerance or allergy, damaging your gums with a toothbrush or irritating toothpaste, and feeling tired, stressed or anxious.

Sometimes they are triggered by things you cannot always control: hormonal changes such as during pregnancy, your genes (some families get mouth ulcers more often), a vitamin deficiency such as iron, zinc, folic acid, vitamin B or vitamin D, medicines including some NSAIDs, beta blockers or nicorandil, and stopping smoking.

Oral Health Foundation describes recurrent aphthous stomatitis, where people get mouth ulcers repeatedly even when otherwise healthy, saying the exact cause is not known, that it is not infectious and not usually inherited, and that it is most common in children, teenagers and young adults.

"Canker sore" is the term used in some places for a mouth ulcer. The NHS says mouth ulcers are common, rarely a sign of anything serious, and may be uncomfortable to live with. Oral Health Foundation describes them as small, painful sores inside the mouth, usually red, yellow or white with a red edge.

The NHS says they usually appear inside the mouth on the cheeks or lips, can appear on the tongue, and you may have more than one at a time.

Oral Health Foundation says minor ulcers are the most common type. They usually appear on the cheeks, lips, tongue or gums, are about the size of the tip of a pencil, may appear in small clusters and usually heal within 1 to 2 weeks. Major ulcers are less common but more severe: larger and deeper, often very painful especially when swallowing, can appear near the tonsils and may take several weeks to heal.

Very rarely, people may develop many tiny ulcers at once, sometimes dozens, which usually heal within 1 to 2 weeks.

The NHS says mouth ulcers are not contagious and should not be confused with cold sores. Cold sores appear on the lips or around the mouth and often begin with a tingling, itching or burning sensation, though they can also appear as a small group of pinhead-sized ulcers inside the mouth.

Oral Health Foundation says mouth ulcers cannot be passed on by kissing or sharing cups, cutlery or food.

The NHS says that if you have several mouth ulcers, it can be a symptom of hand, foot and mouth disease (which also causes a rash on the hands and feet), oral lichen planus (a white, lacy pattern inside the cheeks), Crohn's disease or coeliac disease, or a weakened immune system from a condition like HIV or lupus.

It says to see a GP if you also have ulcers anywhere else on your body, such as your skin or genitals, or painful, red or swollen joints. Oral Health Foundation says mouth ulcers can sometimes be the first sign of another health condition, such as anaemia, vitamin deficiencies or digestive or skin conditions.

The NHS says that although most mouth ulcers are harmless, a long-lasting mouth ulcer is sometimes a sign of mouth cancer, so it is best to get it checked. Its mouth cancer page lists a mouth ulcer that lasts more than 3 weeks, a red or white patch, a lump in the mouth or on the lip, mouth pain that does not go away, difficulty swallowing or speaking, a hoarse voice that does not go away, a lump in the neck or throat, and weight loss without trying.

It says these symptoms are very common and can be caused by other conditions, but that finding cancer early may mean it is easier to treat, and that a dentist can also help with ulcers, lumps, patches or pain in your mouth.

The NHS says to see a dentist or GP if your mouth ulcer lasts longer than 3 weeks, is different to other mouth ulcers you have had before (for example bigger than usual or near the back of your throat), or bleeds or becomes more painful and red, which may be a sign of an infection.

Oral Health Foundation adds that you should seek advice if ulcers keep coming back, you feel unwell or have other symptoms, or the ulcer is very painful or getting worse.

Most mouth ulcers can be managed with self-care and pharmacy advice. For persistent, severe or recurrent ulcers, a dentist or GP can examine the mouth and prescribe stronger treatment or arrange tests.

Some people choose a private dentist or oral medicine specialist for recurrent ulcers. Ask what the likely cause is, whether tests such as blood checks for deficiencies are needed, and what to do if an ulcer lasts beyond 3 weeks.