Mouth Ulcers (Canker Sores): Causes and What Helps

Mouth ulcers, also called canker sores, are small, round, painful sores inside the mouth. They have a white or yellow centre and a red edge. They are not catching, and most heal on their own in one to two weeks. See a doctor if one lasts more than three weeks. This guide is by Dr. Pedro Yelamo Vera, an English-speaking GP licensed in Spain (Colegiado No. 484814280) who sees patients by video in English and Spanish.

What are mouth ulcers?

They are shallow sores inside the mouth. In the US they are often called canker sores. Doctors call them aphthous ulcers. In Spain the word is afta or llaga en la boca.

They are usually oval and a few millimetres wide. They have a white or yellow base and a red ring around it. They sting when you eat, drink something sour or brush your teeth. You can get one or several at a time. Most are small and leave no mark.

What causes mouth ulcers?

Often there is no clear cause, but there are known triggers:

• biting your cheek, braces, dentures that rub, or a sharp tooth;
• a burn from hot food, or brushing too hard;
• stress, tiredness or hormone changes, for example around a period;
• low iron, vitamin B12 or folic acid;
• some medicines, such as certain anti-inflammatory painkillers or beta blockers;
• stopping smoking, which can bring them on for a few weeks;
• some toothpastes with sodium lauryl sulphate (SLS).

If many appear at once or they keep coming back, they can be a clue to another illness. Examples are coeliac disease, Crohn's disease or a weak immune system. So it is worth telling a doctor.

How do you get rid of a mouth ulcer?

Most heal by themselves. At home the aim is to ease the pain and avoid making the sore worse while it heals.

• Use a soft toothbrush and a toothpaste without SLS.
• Avoid very spicy, salty, sour or crunchy food, and very hot drinks or fruit juice.
• Drink cool drinks, with a straw if it hurts.
• Rinse with warm water and a little salt.
• At the pharmacy you can ask for an antiseptic mouthwash, or a gel or spray for the pain. Follow the leaflet.

If the ulcers are large or come back often, a doctor may suggest another treatment, such as a steroid made for use in the mouth. There is no single plan for everyone.

Is it a mouth ulcer or a cold sore?

A mouth ulcer forms inside the mouth and is not catching. A cold sore forms outside, on the edge of the lip. It starts with tingling and small blisters that then crust. A virus causes it, and it does spread. If you think it is a cold sore, read about cold sores and their treatment.

Are mouth ulcers contagious?

No. You cannot pass on a mouth ulcer by kissing or sharing a glass. Some sores that look alike do spread, such as cold sores or hand, foot and mouth disease, which is common in children.

Why do I keep getting mouth ulcers?

Some people get ulcers again and again, often from childhood, and it can run in the family. It tends to get better with age.

If you get them several times a year, a doctor may order a blood test. It checks iron, vitamin B12 and folic acid, and sometimes tests for coeliac disease. It helps to note when they appear and what you ate or what changed before.

What about mouth ulcers in children?

Children get mouth ulcers too. Fever, many sores in the mouth and spots on the hands or feet may mean a viral infection. The key thing is that they keep drinking. A child who will not drink because of the pain, passes little urine or seems very unwell needs to be seen.

What do I ask for at a Spanish pharmacy?

Say tengo aftas or tengo una llaga en la boca. You can ask for a colutorio antiséptico (antiseptic mouthwash) or a gel para las aftas. The pharmacist will tell you how to use it.

When to see a doctor

• An ulcer lasts more than 3 weeks. Other causes, including mouth cancer, need to be ruled out.
• A sore does not hurt, or a white or red patch will not go away.
• Ulcers are very large, bleed, or get more red and painful.
• Many ulcers appear at once with a fever or you feel unwell.
• You also have sores on the genitals, skin or eyes, or sore, swollen joints.
• You have diarrhoea, weight loss or tiredness as well.

When to call 112

• The lips, tongue or throat swell and you find it hard to breathe.
• You cannot swallow your saliva or you are drooling a lot.
• A child is very unwell, will not drink at all, or shows signs of severe dehydration.

Frequently asked questions about mouth ulcers

Getting a medical assessment

If you are in Spain and have mouth ulcers that keep coming back, or a sore that will not heal, you can book a video consultation with Dr. Pedro Yelamo Vera, a physician registered in Spain. You can also read about aciclovir for cold sores. A prescription is never guaranteed: it is issued only where clinically appropriate after a genuine evaluation, as a private electronic prescription under Spanish law. This service is for urgent, non-emergency care. In an emergency, call 112.

This guide is general information. It does not replace the package leaflet or the advice of your doctor or pharmacist.