What causes mouth ulcers

What causes mouth ulcers?

Most of us have experienced the irritation of a mouth ulcer at some point. These painful spots – also known as canker sores – are small round lesions which appear white in colour with a faint red border. They can develop anywhere on the inside of our cheeks, inner lips, tongue and gums.

Maybe you are prone to mouth ulcers and seem to get them all the time – or maybe you’ve just got your first one in years. They can be pretty painful – but are almost always harmless.

Read on to find out what causes them, and who might be particularly prone to developing them.


The tissues inside your mouth are sensitive. Something as simple as over-zealous brushing can cause minor damage to the oral mucosa (the wet skin layer lining your mouth).

Other things which cause injury to the mouth, such as accidentally biting the inside of your cheek or tongue or being hit by the ball during sports, disrupt these delicate tissues and can lead to a mouth ulcer. These are known as traumatic ulcers.

Another common cause of mouth ulcers is food that’s too hot, causing scalding to the mouth or tongue. Food that’s particularly acidic or spicy can also trigger them.

Crisp-lovers should watch out, too, as spiky, sharp foods are also known causes of mouth ulcers due to the micro-injuries they can inflict on the oral mucosa as we crunch them.


Wearing dental braces, retainers or false teeth are all common causes of traumatic mouth ulcers especially along the gum line. Speak to your dentist or orthodontist if you experience recurring mouth ulcers, as they can be a sign your dental device doesn’t fit properly and is rubbing.

Similarly, oral piercing such as to the lip or tongue, can be a risk factor for recurring mouth ulcers due to the jewellery causing irritation to the delicate oral tissues.

Anxious habits such as chewing the inside of your cheek could also be at the root of mouth ulcers in the absence of any clear medical explanation.


Being short of certain vitamins and minerals can cause issues in and around the mouth. Low levels of iron (anaemia), and a deficiency of zinc and B vitamins, including vitamin B12 have been linked to mouth ulcers1.


Stress is a contributory factor in a whole range of minor ailments, and mouth ulcers are no different. A high-stress lifestyle, which can include lack of sleep and no time for relaxation, can trigger an outbreak of mouth ulcers if you’re already prone to them.

A 2017 study in Iran on 54 volunteers found that recurrent aphthous stomatitis (RAS) was linked to high levels of both anxiety and depression in sufferers2.

Gut inflammation

Your mouth can mirror what’s going on in your gut. This is why bad breath is often a side effect of gut imbalances and acid reflux. Yes - your gut and mouth are directly linked, and the latest research shows that they share some of the same microbial species3.

Disorders such as Coeliac disease (an intolerance to gluten) and inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease are some of the more serious causes behind mouth ulcers. Inflammatory bowel diseases can only be diagnosed by a doctor.

This is because they cause inflammation in your digestive system – of which your mouth is a part.

However, these conditions are not usually the cause of mouth ulcers in absence of other symptoms – so don’t worry.


It’s relatively rare to experience a mouth ulcer which is caused by an infection. Luckily, this means they’re not contagious.

However, if you get multiple mouth ulcers at once and they keep coming back (more than a couple of times a year) it might be classed as recurrent aphthous stomatitis (RAS). In these cases, the mouth ulcer might be a secondary symptom of a viral or bacterial infection4.

This is a rarer symptom of herpes simplex – so mouth ulcers alone are no cause for alarm. Consult your doctor if you’re unsure.

Who can get mouth ulcers?

Anyone can experience a mouth ulcer at any time. There is not always a clear reason as to why they appear.

However, it seems that certain people are susceptible to getting them. Genetics plays a significant role – getting frequent mouth ulcers seems to run in families5.

Last updated: 29 April 2020

Gum HealthLip CareSkincare