Canker sores often do not have one identifiable cause. A small injury inside the mouth, stress, certain nutritional deficiencies, and other factors may help trigger a sore in some people, but a trigger is not always found. If sores are frequent, unusually severe, or slow to heal, a dentist or medical professional can check whether something else may be contributing.
What a canker sore is
A canker sore, also called an aphthous ulcer, is a painful sore that forms inside the mouth. It often looks round or oval, with a pale center and a red border. Common locations include the inside of the lips or cheeks and the tongue.
Canker sores are not contagious. They are also different from cold sores, which are associated with the herpes simplex virus and commonly occur around the lips. Still, a description or photo cannot confirm what a particular sore is. Several conditions can cause changes inside the mouth, so it is sensible to have a sore checked when its pattern is unusual or it does not heal as expected.
Why the cause can be hard to pin down
The exact cause of canker sores is unknown. That is why it is more accurate to talk about possible triggers and contributing factors than to assume that one event caused a sore.
Authoritative health guidance identifies several possibilities:
- Minor injury or irritation. Biting the cheek, rough brushing, dental work, braces, a rough filling, or a sharp tooth can irritate the soft lining of the mouth.
- Stress or tiredness. Some people notice sores during stressful periods, although timing alone does not prove that stress was the cause.
- Nutritional deficiencies. Low levels of iron, folate, or vitamin B12 may be associated with recurring sores in some people. A sore by itself does not show that a deficiency is present.
- Food-related irritation or sensitivity. Certain foods may be associated with a flare for some people, while spicy, acidic, hot, or rough foods can make an existing sore feel worse.
- Hormonal or immune factors. These may contribute in some cases, but they are not something a reader can identify from the sore alone.
Sometimes sores recur without an obvious trigger. A pattern may still be useful information even when it does not provide a diagnosis.
What you can notice without trying to diagnose the sore
If sores keep returning, a short, simple record can make a dental or medical conversation more useful. You might note:
- when the sore appeared and when it healed;
- where it formed;
- whether there was recent biting, dental work, or another source of friction;
- whether there were several sores at once;
- whether eating or drinking became difficult; and
- whether other symptoms appeared elsewhere in the body.
This kind of record is not a self-test. Its purpose is to show the pattern accurately, especially if each sore has healed by the time of an appointment.
Making an ordinary sore less irritating
Many canker sores heal on their own within about one or two weeks. While a sore is healing, avoiding foods or drinks that sting or scrape the area may make eating more comfortable. A soft-bristled toothbrush can also reduce extra irritation.
Be cautious about treating a recurring sore as proof of an allergy, vitamin deficiency, infection, or other condition. Supplements and medicines can have risks and may not address the real reason for the sores. A pharmacist, dentist, or medical professional can help you discuss symptom relief or whether an assessment is appropriate.
When a mouth sore should be checked
Arrange a dental or medical assessment if a sore lasts longer than three weeks, is different from your usual sores, becomes more painful or red, bleeds, or keeps returning. It also deserves attention when sores are severe enough to make eating or drinking difficult, or when they occur with joint symptoms or ulcers elsewhere on the body.
Most mouth ulcers are not serious, but a long-lasting ulcer can have causes other than a canker sore. If you want more context about a related dental examination, learn what an oral cancer screening involves.
The practical takeaway
Canker sores are common, painful, and usually short-lived. Their exact cause is often uncertain. Rather than blaming one food or assuming a deficiency, notice the pattern, reduce obvious irritation, and seek professional assessment when sores are persistent, unusual, frequent, severe, or accompanied by other symptoms.
Sources
- Fever Blisters & Canker Sores — National Institute of Dental and Craniofacial Research
- Canker Sores — MouthHealthy, American Dental Association
- Mouth ulcers — NHS