Mouth ulcers - Causes 

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


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The 11 comments posted are personal views. Any information they give has not been checked and may not be accurate.

paganini said on 27 July 2014

I had mouth ulcers all my life (I'm 35), they could be anywhere including inner area of lips. Sometimes they were so bad that I could not eat without tears, or speak for weeks.

GPs did not know what to do and kept referring me to a dentist, who would refer me back to GP!

looks like this is absolutely unstudied subject

but recently I discovered that all these was probably caused by dairy products! I'm dairy free for 3 months now, and haven't had any ulcers for 3 months!

hope this will help others to find their triggers too

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NANA1212 said on 29 November 2013

As for this continue My wife sister she had problem in mouth and ear. and sometimes hard to swallow the food but never worry her because she never ever think about cancer. As she never smoke hardly drink and visit dentis every 3 month. She eat chili a lot in her life which doc said that its might be cause to aggravate her ulcer in cancer. As for my experience that i want to urge people that please if you smoke and drink a lot ..please stop this otherwise if you have this problem you have more chance to get mouth cancer then others.

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NANA1212 said on 29 November 2013

I m 33 yr healthy male as I dont have ulcer problem in my life. But back in 9 month ago I got ulcer in under right side of lip. In beginning of 2 weeks I wouldn't care as nothing bother me. But after six weeks the same thing is there. But I never hurt or like that. My wife told me to show to doctor which I m always avoid her call. But after 8 weeks I showed GP and she told me it might be ulcer but told me to show dentist. As it not heal I m so much in tension but worry a lot to show dentist. After 11 weeks the same problem as I never other problem in mouth. As my eating and drinking habit as I eat normal food, never smoke and start drink one year before. And when I showed to dentist he told me straight away to show dental school because he bit suspisous about this thing and it wouldnt heal after a long time. That call of dentist make sure to me that I have to face worst in future. When I show to dental school they told me to do biopsy which I did and have to wait for result. As it coincidence or what as my wifes sister she had did its biopsy the next day which I did mine. She had ulcer in her tongue. Which she has same period of time as mine or may be less. We always talk about this which I consider my self serious then her as she fell the same way of her ulcer. When the result has come after may be 18 weeks or so I m mostly sure that I got mouth cancer because after a long period it not heal but lucky enough the doctor told me that I have just Ulcer make me relief a lot because during this time I feel strees a lot. As My wife sister she never smoke eat normal food and she drink occasionally. And about her result she got cancer on her tongue. We so much sad about her result that because its really hard to believe that she got this problem. She already did surgery as they cut little part of her tongue. As I want to tel you here in my experience that I had this ulcer long time but I never had problem in mouth, neck or ear.

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NoFear said on 03 November 2013

Good to learn to your journal. Im having a mouth ulcer once my back feels cold. Also when, I move here in shanghai, I kept on having a mouth ulcer and i dont know the reason. Sometimes, I have three big mouth ulcer. I dont know how cure to stop this. It make me sick if i have this...

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Riridrozzer said on 10 October 2013

That's interesting because I have coeliac disease, and I was diagnosed about 3/4 months ago, and I have a mouth ulcer, but I don't think it will be affected by the gluten intolerance will it? I'm on a 100% gluten free diet.

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Sillen said on 29 April 2013

I am getting them from E120 (red food color) also named Carmine, Kochinel etc. A few days after I've eaten E120 I'm surtain to get painfull mouth ulcer.

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kittykatkin said on 15 August 2012

Crisps always cause mouth ulcers for me. It probably is the sharp edges but it seems to be worse for me if they are more flavoured, for want of a better word. Meaty flavoured crisps are almost guaranteed to give me an ulcer. I love them too much to avoid though, despite the fact they also give me heartburn too!

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chrisgg said on 16 May 2012

Interesting...I drink cocoa regularly and have been eating a lot of nuts recently, including raw almonds and roasted peanuts. Maybe this is why I have been getting ulcers frequently.
Most people eat tomatoes, cheese and wheat flour with no problem(think pasta and pizza). Of course any acid food will hurt an ulcer already formed.
I would think it logical that it is the shards of nuts in the mouth while you crunch into them (especially raw almonds) that might damage the delicate skin of the cheeks and tongue....or while biting forcefully into the nuts, perhaps you nip the sides of the mouth or tongue.

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cameron arless said on 08 January 2012

another thing that could cause mouth ulcers ie
- crisps - sharp edges on certain types of crisps

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kittywoo said on 27 October 2011

I would also add chewing gum to the list of foods to avoid, specifically sugar free. I can guarantee that if I have one piece of gum the following day I will have a mouth ulcer at the back of my mouth.

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Mimi Pinson said on 07 January 2011

To the foods to be avoided, I would add:
- Deep fried food (home shallow fried food is fine)
- Cakes and biscuits
- Cream

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