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Causes of mouth ulcers

NHS Choices Medical Reference

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Mouth ulcers aren't usually infectious, which means they can't be passed from person to person.

So, you won't get a mouth ulcer from kissing someone who has one, or by sharing drinking glasses or cutlery with them.

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, by using a toothbrush incorrectly, or from a sharp tooth, food or filling.

Other causes of more troublesome mouth ulcers, or ones that keep coming back, include:

Stress and anxiety

Some people find they develop mouth ulcers during times of stress or when they're feeling particularly anxious.

Hormonal changes

Some women develop mouth ulcers during their monthly period.

Family history

Around 40% of people who have recurrent mouth ulcers report that it runs in their family. 

Food triggers

Eating certain foods can increase your likelihood of mouth ulcers. Culprit foods include:

  • chocolate
  • coffee
  • peanuts
  • almonds
  • strawberries
  • cheese
  • tomatoes
  • wheat flour

Stopping smoking

When you first stop smoking, you may find that you develop mouth ulcers. This is a normal reaction. Your body is dealing with the change in chemicals in your body.

After giving up smoking, any increase in mouth ulcers will be temporary, so don't let it put you off stopping smoking. The long-term health benefits of not smoking are far greater than the short-term discomfort of mouth ulcers.

Medical conditions

If you have mouth ulcers that keep returning, they may be caused by an underlying medical condition such as:

  • Vitamin B12 deficiency: a lack of vitamin B12 can cause tiredness, shortness of breath and mouth ulcers.
  • Iron deficiency: if your diet is lacking in iron, your red blood cells are unable to carry as much oxygen. This can make you feel tired, lacking energy and dizzy. Sometimes, an iron deficiency can also cause mouth ulcers.
  • Coeliac disease is caused by intolerance to a protein called gluten, which is found in wheat, rye and barley. The condition causes the small intestine to become inflamed. Mouth ulcers are also a common symptom of coeliac disease.
  • Crohn's disease is a condition that causes inflammation of the gut, leading to ulcers developing in both your stomach and mouth.
  • Reactive arthritis is a reaction to another infection within your body. It can cause inflammation, which sometimes spreads to your mouth.
  • Immunodeficiency: any condition, such as HIV or lupus, that attacks or suppresses the body's immune system can cause you to develop mouth ulcers.


Occasionally, mouth ulcers are caused by a reaction to a medicine that you are taking. Some of the medicines that can cause mouth ulcers include:

  • Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin.
  • Nicorandil, a medicine which  is sometimes used to treat angina.
  • Beta-blockers, which  are used to treat a variety of conditions that affect the heart and blood flow, such as angina, heart failure, high blood pressure and abnormal heart rhythms.

You may notice that you start to get mouth ulcers when you begin taking the medicine, or when you increase the dosage.

Speak to your GP if you think your medication is causing your mouth ulcers. You may be able to take an alternative medication.

Less common causes

There are also other, less common causes of mouth ulcers.

Now read about how to treat mouth ulcers.

The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Medical Review: April 21, 2012

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