Causes of mouth ulcers 

Most minor, single mouth ulcers are caused by damage to the mouth, for example by accidentally biting the inside of your cheek while you are eating or from a sharp tooth, food or filling.

These ulcers will usually heal within a week or two and are not a sign of any serious problem.

Causes of recurrent mouth ulcers

The cause of mouth ulcers that keep coming back is not always clear. It is thought that your genes may make you more likely to develop mouth ulcers as a result of certain triggers, as around 40% of people who have recurrent mouth ulcers report that it runs in their family.

Some of the factors that may trigger recurrent mouth ulcers include:

  • stress and anxiety 
  • hormonal changes – some women develop mouth ulcers during their monthly period
  • eating certain foods – such as chocolate, coffee, peanuts, almonds, strawberries, cheese, tomatoes and wheat flour
  • toothpaste additives – it has been suggested that the additive sodium lauryl sulphate, found in some toothpastes, may cause or aggravate mouth ulcers in some people
  • stopping smoking – when you first stop smoking, you may find you develop mouth ulcers (as a result of your body dealing with the change in chemicals in your body)

If you are trying to stop smoking, don't be put off if you develop mouth ulcers. Remember that the mouth ulcers are temporary, and the long-term health benefits of not smoking are far greater than the short-term discomfort of the ulcers. Read more about stopping smoking.

Medical conditions

In some cases, recurrent mouth ulcers may be a sign of an underlying medical condition, such as:

  • viral infections – including the cold sore virus (herpes simplex), hand, foot and mouth disease and chickenpox
  • vitamin B12 deficiency – where a lack of vitamin B12 causes the body to produce abnormally large red blood cells that cannot function properly
  • iron deficiency – where a lack of iron in your blood leads to a reduction in the amount of oxygen reaching your organs and tissues
  • coeliac disease – a common digestive condition where a person has an adverse reaction to gluten
  • crohn's disease – a long-term condition that causes inflammation of the lining of the digestive system
  • reactive arthritis – a condition that causes inflammation in various places in the body, usually as a reaction to an infection
  • lichen planus – a non-infectious, itchy rash that can affect many areas of the body
  • Behçet’s disease – a rare and poorly understood condition that causes inflammation of the blood vessels
  • immunodeficiency – when the body's immune system is attacked or suppressed, for example in HIV or lupus  

Medications and treatments

Mouth ulcers can sometimes be caused by a medication you are taking or treatment you are having, such as:

You may notice that you start to get mouth ulcers when you begin your treatment, or when your dosage is increased.

Speak to your GP or care team if you think your treatment is causing your mouth ulcers. You may be able to take an alternative medication or you may be offered medication to treat the ulcers until you finish your course of treatment.

Could it be mouth cancer?

In a few cases, a long-lasting mouth ulcer can be a sign of mouth cancer. Ulcers caused by mouth cancer usually appear on or under the tongue, although they can appear elsewhere in the mouth.

You are more at risk of developing mouth cancer if you are male, over 45 years old and you smoke or drink heavily.

If mouth cancer is detected early, the chances of a complete recovery are good. This is why it is always important to have regular check-ups with your dentist. They can carry out a thorough assessment of your teeth and mouth, and will be able to spot any possible signs of mouth cancer.


Page last reviewed: 06/03/2014

Next review due: 06/03/2016