Mouth Ulcers and Canker Sores: Causes and Healing Course

Sores that appear inside the mouth from time to time are a common experience for many people. A large share of them are the small, painful ulcers commonly known as canker sores (aphthous ulcers). They usually heal on their own and are not contagious; even so, the discomfort they cause while eating and speaking makes them a frequent topic at dental examinations.

This article outlines the general features of canker sores, the triggers that may play a role in their appearance, how they differ from cold sores, and their healing course. The content is for information purposes; the cause of a sore in the mouth can only be assessed through a clinical examination.

What Is a Canker Sore and What Does It Look Like?

A canker sore is a shallow ulcer that forms in the soft lining of the mouth. It is usually round or oval, covered by a whitish-yellow layer in the centre and surrounded by a red halo. The inner cheeks, inner lips, edges of the tongue and the floor of the mouth are the areas where it is most often seen.

Most canker sores stay a few millimetres wide and appear one at a time. Larger, deeper forms, or episodes with many small sores at once, may also be seen. The sore may sting or burn on contact with acidic, salty or hot foods; this usually eases as healing progresses. Canker sores are not contagious; they do not pass to another person through shared glasses or cutlery.

Possible Triggers

No single, definite cause of canker sores has been identified; several factors are thought to act together. Minor injuries such as cheek biting, hard brushing, a sharp tooth or filling edge and orthodontic appliances are among the commonly mentioned triggers. Acidic and spicy foods, as well as some toothpaste ingredients, may also make sores more likely in some people.

Stress, fatigue, disrupted sleep and hormonal changes are also among the factors associated with episodes of canker sores. Certain deficiencies, such as iron, vitamin B12 and folate, are known to accompany frequently recurring sores; the effect of eating habits on the oral tissues is discussed separately in nutrition and gum health. Which trigger stands out varies from person to person.

Systemic Conditions and Frequently Recurring Sores

Most canker sores are linked to local triggers and are not a sign of a general health problem. However, sores that recur very often, appear in large numbers or are larger than usual may accompany systemic conditions such as Behcet's disease, coeliac disease, certain bowel diseases and conditions affecting the immune system.

This possibility does not apply to everyone who has canker sores. The frequency and duration of the sores and any accompanying findings are considered together during the dentist's assessment; where needed, a referral to the relevant medical specialty can be made.

The Difference Between Canker Sores and Cold Sores

Although the two are sometimes used interchangeably in everyday language, canker sores and cold sores are different conditions. A cold sore is a contagious condition associated with the herpes simplex virus; it usually appears at the edge of the lip or on its outer surface. It starts as small fluid-filled blisters, which then break open and heal by crusting over.

A canker sore, on the other hand, appears directly as a shallow ulcer on the movable soft tissue inside the mouth, without a blister stage, and it is not contagious. In addition, cold sores tend to recur in the same area from time to time, whereas canker sores may appear in different places inside the mouth. Location and appearance often help tell them apart, but the distinction is not always straightforward; where in doubt, an assessment by a dentist is appropriate.

Healing Course and When to See a Dentist

Most canker sores heal on their own within about one to two weeks without leaving a scar. During this period, avoiding acidic and spicy foods and continuing gentle cleaning with a soft brush may reduce discomfort; the use of soothing products is guided by the dentist's advice. Sores and tenderness related to irritation at the gum line can be assessed through a periodontal examination and, where needed, within the scope of gum treatment.

A sore that lasts longer than two weeks, shows no tendency to heal, keeps growing, or persists despite being painless calls for a different approach. Such a sore does not usually point to a serious condition, but it is important that a dentist examines it so that its cause can be clarified. When a sore of this kind is noticed, informing the clinic is appropriate.

In Summary

The frequency, duration and triggers of canker sores, and the discomfort they cause, vary from person to person. Whether a sore in the mouth is a canker sore or a finding belonging to another condition only becomes clear through a clinical examination and, where needed, further tests.

This content has been prepared for general information purposes and does not replace an individual assessment; consult your dentist for accurate information.