Mouth Ulcers (Canker Sores): When Should You Worry?

A canker sore (aphthous ulcer) is a round or oval, painful, shallow sore inside the mouth with a whitish-yellow center and a red border. Most canker sores heal on their own within 1–2 weeks. However, mouth sores that last longer than 2 weeks, keep growing or recur frequently need to be assessed by a doctor or dentist.

What is a canker sore?

A canker sore is a non-contagious, painful, shallow sore that appears on the lining of the mouth; in the medical literature, its recurrent form is called recurrent aphthous stomatitis. It is usually seen on the inner surfaces of the cheeks and lips, on the sides of the tongue or on the floor of the mouth. It should not be confused with a cold sore (herpes); a cold sore usually starts as small blisters on the outside of the lip and is contagious.

Canker sores are divided into three groups according to their appearance and duration:

• Minor canker sores: The most common type. They are usually smaller than 1 cm and heal within 1–2 weeks without leaving a scar.
• Major canker sores: Larger than 1 cm, deeper and more painful. Healing can take weeks and may leave a scar.
• Herpetiform ulcers: Characterized by many very small sores appearing together, which may merge over time.

Why do canker sores appear?

The exact cause of canker sores is not known; however, the immune system's response to certain triggers is thought to play a role. They are more common in people with a family history of canker sores. Known triggers include:

• Minor injuries: Biting the cheek, brushing too hard, a sharp tooth edge, an orthodontic appliance or an ill-fitting denture,
• Stress and irregular sleep,
• Certain foods: In some people, acidic fruits, spicy foods or nuts,
• Toothpaste ingredients: Toothpastes containing sodium lauryl sulfate can trigger canker sores in some people,
• Hormonal fluctuations,
• Nutritional deficiencies: Iron, vitamin B12 or folic acid deficiency,
• Systemic diseases: Celiac disease, inflammatory bowel diseases, Behçet's disease and some conditions affecting the immune system.

When canker sores recur frequently, these underlying conditions may need to be investigated; when necessary, this assessment is carried out together with the relevant medical specialists.

How long does a canker sore last?

Minor canker sores usually heal on their own within 7–14 days without leaving a scar. The pain is often most intense in the first few days and then gradually eases. With major canker sores, this period can extend to several weeks.

In some people canker sores recur a few times a year, in others more often. It is commonly observed that canker sores that begin in childhood and adolescence become less frequent with age. Noting when your canker sores appear, how many days they last, what you ate beforehand and whether you were going through a stressful period helps you recognize your triggers and give your doctor clearer information.

For this reason, healing time is an important criterion in assessing a mouth sore. A sore that shows no sign of healing within the expected time may be due to a cause other than a canker sore and should be examined.

How can you ease a canker sore at home?

There is no single method that speeds up the healing of a canker sore; what you can do at home is aimed at reducing pain and protecting the area from irritation:

• Keep up your oral care; brush with a soft-bristled brush without putting pressure on the sore.
• Avoid spicy, sour, salty, very hot and sharp-edged foods for a while.
• Rinsing your mouth with warm salt water may be soothing.
• You can use protective gels or mouth rinses available at pharmacies on the recommendation of a doctor or pharmacist.
• If you get canker sores often, trying a toothpaste free of sodium lauryl sulfate may be helpful.
• If a sharp tooth edge or a denture is constantly irritating the sore, show it to your dentist.

Applying irritating substances such as alcohol, salt or lemon to a canker sore can irritate the tissue further; it is recommended that you avoid home remedies of this kind. If pain is significantly reducing how much you eat and drink, make sure fluid intake is adequate, especially in children and older adults, and see a doctor.

Which mouth sores are not canker sores?

Not every sore in the mouth is a canker sore; some sores and patches require a different diagnosis and treatment. Conditions that can be confused with canker sores include:

• Cold sores (herpes): Start with small blisters and are contagious.
• Traumatic sores: Caused by a sharp tooth, a denture or brushing too hard; they are expected to heal once the cause is removed.
• Oral lichen planus: A chronic condition that presents with white lace-like lines, redness and sometimes sores inside the mouth. It can also affect the gums.
• Fungal infection (thrush): Appears as white plaques that can be wiped off.
• White or red patches: White (leukoplakia) or red (erythroplakia) patches that cannot be wiped off must always be assessed.
• Oral cancer: In its early stages it often may not cause pain; it can present as a sore that does not heal, hardness, a raised edge or swelling. Smoking, alcohol and HPV are known risk factors.

Sores and patches on the gums can also be confused with gum diseases. In such cases, an assessment for gum disease is carried out to reach a differential diagnosis.

When should you see a dentist?

Most mouth sores are harmless; however, it is recommended that you see a dentist or doctor in the following situations:

• If the sore lasts longer than 2 weeks and shows no sign of healing,
• If the sore is larger than 1 cm or keeps growing,
• If canker sores recur very often or make it hard to eat and drink,
• If the sore is accompanied by fever, fatigue, weight loss or swelling in the neck,
• If there are white or red patches that cannot be wiped off, hardness or swelling in the mouth,
• If, along with mouth sores, you have genital sores, eye redness or joint complaints,
• If the sore is on the gum and occurs together with gum bleeding or recession.

Periodontist Dr. Nadin Gemrekoğlu, DDS, PhD, examines sores on the gums and the lining of the mouth and, when necessary, arranges further tests or referral to the relevant specialty. To make an appointment, you can reach us through our contact page.