What causes mouth ulcers and how to treat them

What are mouth ulcers?

Mouth ulcers, sometimes called canker sores, are small, painful sores that can develop inside your mouth - inside your cheeks, on the roof of your mouth, on your tongue, or at the base of your gums. They can be raised, and may be red, yellow, white, or grey in colour.

Although they can cause some discomfort and pain - especially when pressed or nudged during eating - mouth ulcers are normally harmless and clear up by themselves within 1-2 weeks.

What causes mouth ulcers?

If you develop a mouth ulcer as a one-off occurrence, the chances are it was caused by a minor trauma. Did you bite your cheek while brushing your teeth? Burn your tongue on a hot drink? Perhaps you have poorly fitting dentures?

In most cases, why some people have mouth ulcers that keep returning is more of a scientific mystery. This is called recurrent aphthous stomatitis, and the cause is not known.

It's thought that whatever causes mouth ulcers triggers an immune system reaction that results in the sore¹. We also know that mouth ulcers aren't infectious - you can't spread them to anyone.

What about mouth ulcer triggers?

Dr Ross Perry is a GP and medical director of Cosmedics. He explains that, while the cause of mouth ulcers isn't fully known, if you keep getting them it's likely that they are being triggered by one of the following factors:

• A weak immune system.

• Stress.

• Dehydration.

• Acidic foods.

When could it be a disease?

Sometimes, mouth ulcers can also be a symptom of another underlying health problem that needs to be identified and treated.

Dr Perry says: "Speak to your GP or dentist if your mouth ulcers gets larger, lasts for more than three weeks, causes you extreme pain, or if you develop a fever."

Can gut conditions cause mouth ulcers?

In rare cases, recurring mouth ulcers could be a symptom of some gastrointestinal diseases, such as Crohn’s disease and coeliac disease. If your mouth ulcers last more than 1-2 weeks and you notice other signs of Crohn's disease or coeliac disease around the same time, speak to your GP about getting tested.

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Can cancer cause mouth ulcers?

Mouth ulcers that last a long time - three weeks or more - are the most common sign of mouth cancer². This type of cancer is usually linked to heavy drinking and smoking, and cancerous ulcers most often appear under the tongue. You should also look out for the other symptoms of mouth cancer.

Remember, though, that this is still a relatively rare cause of mouth ulcers and the only way to know for sure is to get either your dentist or GP to examine the sore/s in question.

How to treat mouth ulcers

As mouth ulcers are usually nothing to worry about, unless you have other concerning symptoms, you can wait to see if they clear up within a week or two.

Alternatively, to ease any pain or discomfort, Dr Perry says that there are self-care soothing methods you can use.

"You can purchase several products over the counter in pharmacies to treat mouth ulcers which will help to not only soothe but also speed up the recovery."

Options include:

• Painkillers - available lozenges, mouthwash, sprays, and gels.

• Antimicrobial mouthwash.

• Corticosteroid lozenges.

"A home method is warm water with half a teaspoon of salt. A good gargle of this will help to relieve any pain," adds Dr Perry.

How to prevent mouth ulcers

If your mouth ulcers are caused by any of the common triggers, Dr Perry says these lifestyle hacks can help keep your mouth ulcer-free.

Further reading

1. Dudding et al: Genome wide analysis for mouth ulcers identifies associations at immune regulatory loci.

2. Macmillan Cancer Support: Mouth cancer.