A mouth ulcer is a sore that appears inside your mouth. They can be red or yellow and vary in size from very tiny to quite large. Often they are round or oval but they can appear in any shape. Mouth ulcers tend to be sore or even painful.


There are loads of possible causes for mouth ulcers. We’ll come back to this at the bottom but it is vital that you visit your dentist if you have an ulcer that does not heal after two weeks or you have ulcers that keep coming back.


One of the most common causes of ulcers is trauma. This might be biting your cheek or tongue when eating. It could be that you have a sharp tooth that rubs the inside of your mouth to make a sore. Or it might be that a sharp bit of food catches you during chewing, cutting the inside of your mouth and causing an ulcer.


Bacterial or viral infections can cause ulcers in your mouth. An ulcer next to a tooth might be caused by bacteria that have infected the tooth. Viruses such as herpes simplex can cause lots of tiny ulcers that can be very sore.


Sometimes an underlying health issue can lead to ulcers in your mouth. Anaemia is a good example. This is when you don’t have enough red blood cells. Anaemia often remains undiagnosed but if you feel constantly tired and suffer from regular mouth ulcers, this could be the cause.

Oral cancer

The first visible sign of oral cancer is often an ulcer that won’t go away. If you smoke or regularly drink alcohol, you have an increased risk of developing cancer in your mouth. However, these are not the only causes of oral cancer. This cancer can be caused by viral infections that you may not be aware of. If you have an ulcer in your mouth that has not healed within two weeks, you must seek advice from your dentist.

‘Recurrent aphthous stomatitis’

Some people develop ulcers but we cannot figure out what’s causing them. These ulcers can be really uncomfortable, especially the larger ones. When someone has ulcers with no obvious cause that keep returning, we call this ‘recurrent aphthous stomatitis’. These ulcers can be big, small or tiny. There can be one, a few or loads.

If you get ulcers that keep coming back, you should visit your dentist or doctor for them to examine your mouth and offer advice.

Treatment of ulcers

This depends on what is causing the ulcers. Often, all you can do is let the ulcer run its course and heal on its own. In that time, try to keep the area clean. A salty mouthwash can helpful but may sting. Use one tumbler of water and a teaspoon of salt, rinse around your mouth and spit out.

If your ulcers are being caused by an underlying illness such as anaemia, diet supplements such as iron may be helpful. In this situation, we would recommend that you speak to your doctor who may want to do a blood test.

Avoid acidic or spicy foods because they will be sore. There may be soothing mouthwashes or tablets that you can be prescribed by a dentist or buy in a pharmacy. If you regularly suffer with mouth ulcers, seek advice from your dentist.

Can I prevent mouth ulcers?

Yes, you sometimes can. A balanced diet and good oral hygiene will keep you and your teeth healthy. It is thought that stress can bring on ulcers so minimising stress may help to prevent them. Regular checks with your dentist will help you to maintain a healthy mouth and avoid decayed or fractured teeth that may cause infections or ulcers.

What should I do if I get an ulcer?

Don’t worry. Most of the time, mouth ulcers will heal on their own.

However, if you regularly get mouth ulcers or you have an ulcer that has not healed after two weeks, you must visit your dentist to have it checked.

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