In most cases, mouth ulcers are not caused by an infection. This means they cannot be passed from person to person. For example, in most cases it is not possible to get a mouth ulcer from kissing someone who has a mouth ulcer, or by sharing drinking glasses or cutlery with them.
Most minor, single mouth ulcers are caused by damage to the mouth. For example, you may damage the inside of your mouth by accidentally biting the inside of your cheek while you are eating. Mouth damage can also occur from using a toothbrush incorrectly, or from a sharp tooth or filling.
Recurrent mouth ulcers
The cause of recurrent (returning) mouth ulcers is often unknown. However, a number of factors may increase your chances of getting recurrent ulcers. These are listed below.
- Stress and anxiety
- Oral trauma, such as excessive tooth brushing, or chewing sharp or hard foods.
- Hormonal changes: some women develop mouth ulcers during their period. This is due to changes in the hormone levels in your body during your menstrual cycle.
Eating certain foods can also increases your likelihood of developing mouth ulcers. Foods that have been identified as increasing the risk of mouth ulcers include:
- chocolate
- coffee
- peanuts
- almonds
- strawberries
- cheese
- tomatoes
- wheat flour
Around 40% of people who have recurrent mouth ulcers have a family history of the condition.
Stopping smoking
When you first stop smoking, you may find that you develop more mouth ulcers than usual. 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, and you should not let it deter you from stopping smoking. The long-term health benefits of not smoking are far greater than the short-term discomfort of mouth ulcers.
Not smoking will significantly lower your risk of developing serious smoking-related conditions, such as heart disease and lung cancer. Your overall level of fitness will also improve greatly.
Underlying conditions
If you have recurrent mouth ulcers, they may be caused by an underlying medical condition, such as those outlined below.
- Vitamin B12 deficiency: vitamin B12 helps to make red blood cells and keeps your body's nervous system healthy. 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 will not be able to carry as much oxygen. This can make you feel tired, lethargic (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 in adults with the 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 that attacks or suppresses the body's immune system (the body’s natural defence against infection and illness) can cause you to develop mouth ulcers. For example, HIV is an immunosuppressant illness.
Medication
Occasionally, mouth ulcers are caused by a reaction to a medicine that you are taking. Some of the medicines that can cause mouth ulcers are listed below.
- Non-steroidal anti-inflammatory drugs (NSAIDs): painkilling medication, such as ibuprofen and aspirin. Children who are under 16 years of age should not be given aspirin.
- Nicorandil is sometimes used to treat angina (chest pain caused by reduced blood flow to the heart).
- Beta-blockers 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. However, this is often only a temporary effect of the medication.
Speak to your GP if you find that you are having more mouth ulcers as a result of your medication. They may be able to prescribe an alternative medicine for you. However, never stop taking medication that has been prescribed for you unless your GP advises you to do so.
Less common causes
There are also a number of other, less common causes of mouth ulcers. Some of these are listed below:
- Herpes simplex infection: a highly contagious virus, also known as the ‘cold sore virus’, which can cause cold sores on the mouth and the genitals.
- Anaemia: a condition that occurs when there is a reduced number of red blood cells or lower concentrations of haemoglobin (a protein found in red blood cells that transports oxygen around the body). Mouth ulcers can also be caused by other blood disorders, although this is rare.
- Iron deficiency, vitamin B12 deficiency or folate deficiency.
- Skin conditions, such as lichen planus (where flat, blue or violet colour skin lesions appear on the skin), and angina bullosa haemorrhagica (blood-filled blisters that turn to ulcers if they burst).
- Gastrointestinal disease: for example, irritable bowel syndrome (IBS) and gastro-oesophageal reflux disease (GORD).
- Pharyngitis: a sore throat.
- Chickenpox: a mild but highly infectious condition that causes an itchy rash, which blisters and becomes crusty.
- Hand, foot and mouth disease: a common, mild illness that is caused by a type of virus known as an enterovirus.
- A reaction to prescribed medication.
Less common bacterial and viral infections can also sometimes cause mouth ulcers, although this is rare.
