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Mouth ulcers: Symptoms, treatment and prevention

Mouth ulcers are sores that appear in the mouth, often on the inside of the cheeks.

Mouth ulcers, also known as aphthous ulcers, can be painful when eating, drinking or brushing teeth.

Occasional mouth ulcers are usually harmless and clear up on their own. Seek medical advice if they last longer than 3 weeks or keep coming back.

Mouth ulcers cannot be caught from someone else.

Up to 1 in 5 people get recurrent mouth ulcers.

Canker sores (also called aphthous ulcers).

Types of mouth ulcer

The main types of mouth ulcer are:

  • Minor ulcers. These are around 2-8mm in diameter and usually clear up in 10 days to 2 weeks.
  • Major ulcers. These are bigger and deeper, often with a raised or irregular border. This type of ulcer can take several weeks to heal and may leave a scar in the mouth.
  • Herpetiform ulcers: This type of ulcer is a cluster of dozens of smaller sores the size of pinheads.

What causes mouth ulcers?

The exact cause of most mouth ulcers is unknown. Stress or tissue injury is thought to be the cause of simple mouth ulcers. Certain foods, including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes and strawberries), can trigger a mouth ulcer or make the problem worse. Sometimes a sharp tooth surface or dental appliance, such as braces or ill-fitting dentures, might also trigger mouth ulcers.

Some cases of complex mouth ulcers are caused by an underlying health condition, such as an impaired immune system; nutritional problems, such as vitamin B12, zinc, folic acid, or iron deficiency and gastrointestinal tract disease, such as coeliac disease and Crohn's disease.

When you first quit smoking, you may develop more mouth ulcers than normal, but this is temporary.

Some medications, including common painkillers, beta-blockers and some chest pain medicines may cause a reaction that leads to mouth ulcers.

What are the symptoms of mouth ulcers?

You may have a mouth ulcer if you have:

  • A painful sore or sores inside your mouth, on the tongue, soft palate (the back portion of the roof of your mouth), or inside your cheeks.
  • Sores in your mouth that are round, white, or grey in colour, with a red edge or border.

In severe mouth ulcer attacks, you may also experience:

How are mouth ulcers treated?

Pain from a mouth ulcer generally lessens in a few days and the sores usually heal without treatment in about a week or two.

If sores are large, painful or persistent, your dentist may prescribe an antimicrobial mouth rinse, a corticosteroid ointment, or a prescription or non-prescription solution to reduce the pain and irritation.

Can mouth ulcers be prevented?

Although there is no cure for mouth ulcers and they often reoccur, you may be able to reduce their frequency with good dental hygiene and by:

  • Avoiding foods that irritate your mouth, including acidic or spicy foods
  • Avoiding irritation from gum chewing
  • Brushing with a soft-bristled brush after meals and flossing daily, which will keep your mouth free of foods that might trigger a sore.

Seek medical advice about mouth ulcers if you have:

  • Unusually large sores
  • Sores that are spreading
  • Sores that last three weeks or longer
  • Intolerable pain despite avoiding trigger foods and taking over-the-counter pain medication
  • Difficulty drinking enough fluids
  • A high fever with the appearance of the mouth ulcer(s)
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