Mouth Ulcers

Causes of mouth ulcers

Causes of mouth ulcers

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. 

  • Herpes simplex infection: this is a highly contagious virus, also known as the "cold sore virus", which can cause cold sores on the mouth and the genitals.
  • skin conditions, such as lichen planus and angina bullosa haemorrhagica.
  • gastrointestinal disease: for example, irritable bowel syndrome (IBS) and gastro-oesophageal reflux disease.
  • sore throat
  • chickenpox
  • Hand, foot and mouth disease

Treating Mouth Ulcers

Most mouth ulcers don't require specific treatment. They usually heal naturally without treatment if they are:

  • Occasional
  • Mild
  • Do not interfere with your daily activities, such as eating

Self-help tips

If you have a mild mouth ulcer, there are some steps you can take yourself to help your ulcer to heal more quickly: 

  • Use a soft toothbrush when brushing your teeth.
  • Avoid eating hard foods, such as toast, and stick to soft foods that are easier to chew.
  • Avoid eating foods that have triggered an ulcer in the past.
  • Reduce your stress levels by doing an activity that you find relaxing, such as yoga, meditation or exercise.

If your ulcer has a specific cause, such as a sharp tooth cutting the inside of your cheek, it will usually heal naturally once the cause has been treated. If you suspect that a sharp tooth has caused an ulcer, visit your dentist so that they can repair it. 


If your ulcer is painful, your GP or Dental Practitioner can prescribe a medication to help ease your symptoms. You can also buy mouth ulcer medicines over the counter without a prescription at your local pharmacy. Speak to your pharmacist about which medicine would be most suitable for you. Some mouth ulcer gels aren't suitable for children under 16. 

Types of medicines used to treat mouth ulcers

Antimicrobial mouthwash

Antimicrobial mouthwash helps to kill bacteria, viruses or fungi that may cause a mouth infection if you're unable to brush your teeth properly. Chlorhexidine gluconate is the most commonly prescribed mouthwash. You normally have to use it twice a day. After using chorhexidine gluconate, you may notice that your teeth are covered in a brown stain. This staining is not permanent, and your teeth should return to their normal colour once you finish the treatment. The best way to prevent staining is to brush your teeth before using chorhexidine gluconate mouthwash. However, after brushing your teeth make sure that you thoroughly rinse your mouth out with water before using the mouthwash. Chorhexidine gluconate mouthwash should not be used to treat infants under two years old.


A corticosteroid is a type of medicine that reduces inflammation. Mouth ulcer medications contain a low dose of corticosteroid to make the ulcer less painful. It's best to start using corticosteroid medication as soon as a mouth ulcer develops. Hydrocortisone is the most commonly prescribed corticosteroid. It comes as a lozenge, which slowly dissolves in your mouth. You usually have to take a lozenge four times a day. Children under 12 years old should see a GP before starting this treatment.


If your mouth ulcer is very painful, your GP/Dental Practitioner may prescribe a painkiller that you can apply directly to your ulcer. Your GP/Dental Practitioner will usually prescribe benzydamine, which can either be taken as a mouthwash or a spray. You will not be able to use benzydamine for more than seven days in a row. The mouthwash form of benzydamine may sting when you first use it, but this should lessen as you continue to use it. However, if the stinging persists, contact your pharmacist or GP. You may also find that your mouth feels numb when you first use the mouthwash. This is normal and the feeling will soon return to your mouth. If you are pregnant, breastfeeding or trying to get pregnant, tell your GP, Dental Practitioner or Pharmacist before taking benzydamine mouthwash. Although all these treatments reduce swelling and discomfort in mouth ulcers that are already present, they won't prevent you developing new mouth ulcers in future.

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