A canker sore is a painful, shallow sore on the soft tissues inside the mouth, with a white or yellow center and a red border. It is not contagious and it is different from a cold sore. Most small canker sores heal within 7–14 days without leaving a scar.
The short answer to how a canker sore heals is: reduce irritation, keep up your oral care and avoid foods that aggravate the sore. Sores that recur often, are large, show no healing within two weeks or last longer than three weeks should be assessed by a dentist.
What Is a Canker Sore?
A canker sore is a sore inside the mouth known medically as an aphthous ulcer. It usually appears on the inner surface of the cheek and lip, on the tongue, on the floor of the mouth or on the soft palate. Burning and tenderness may be felt at first. An open, round or oval sore then appears.
The white or yellow layer seen over a canker sore does not mean infection. This appearance can come from the tissue covering the surface of the sore as it heals. A canker sore does not usually form fluid-filled blisters.
| Feature | Canker Sore | Cold Sore | Traumatic Sore |
|---|---|---|---|
| Location | Inside the mouth, on soft tissues | Usually around the lips | Where the tissue was bitten or irritated |
| Appearance | Sore with a white-yellow center and a red border | Clusters of fluid-filled blisters | Shape varies with the source of irritation |
| Contagious | Not contagious | Can be contagious | Not contagious |
| Cause | The exact cause often cannot be identified | Herpes simplex virus | Biting, a sharp tooth or an ill-fitting appliance |
| Course | Small types usually heal in 1–2 weeks | Crusting and recurrence can occur | Expected to heal once the irritation is removed |
What Are the Symptoms of a Canker Sore?
A canker sore can cause pain that varies with its size. Even a small sore can make speaking, chewing or brushing your teeth difficult. Symptoms can begin one or two days before the sore appears.
- Burning, stinging or tingling where the sore will appear
- A shallow, round or oval sore
- A white, yellow or gray center
- Redness around the sore
- Pain that increases with sour, spicy, salty or hot foods
- Tenderness when speaking, chewing or swallowing
Canker sores can be classified by their clinical appearance as minor, major and herpetiform. Despite the name herpetiform, this type is not caused by the herpes virus.
| Type of Canker Sore | General Appearance | Healing Process |
|---|---|---|
| Minor canker sore | Usually smaller than 1 centimeter and shallow | Mostly heals in 1–2 weeks without a scar |
| Major canker sore | Can be wider, deeper and more painful | Healing can take several weeks and may leave a scar |
| Herpetiform canker sore | Many small sores appear in clusters | Small sores can merge into a wider area |
Why Do Canker Sores Appear?
Why do canker sores appear? There is no single answer to this question that applies to every patient. Recurring canker sores are thought to be related to the immune response, genetic predisposition, environmental triggers and injuries inside the mouth.
Things That Irritate the Inside of the Mouth
Biting your cheek or tongue, brushing hard, a sharp tooth edge and a rough filling can injure the inside of the mouth. Ill-fitting dentures and orthodontic wires can also cause constant irritation at the same spot.
Hard foods, foods with sharp edges and very hot, sour or spicy foods can make an existing sore more painful. Some people notice that their canker sores recur after certain foods. However, the relationship between food and canker sores is not the same for everyone.
Stress and Everyday Factors
Emotional stress, tiredness and disrupted sleep can coincide with bouts of canker sores in some people. This relationship varies from person to person. Stress alone should not be accepted as the explanation for every recurring mouth sore.
Some toothpastes containing sodium lauryl sulfate can be a trigger in sensitive people. If you think your canker sores are linked to a particular product, a change of formula can be tried after speaking to your dentist.
Nutritional Deficiencies and Systemic Conditions
Frequently recurring canker sores can sometimes be related to a deficiency of iron, folate, vitamin B12 or zinc. Rather than taking vitamins at random, it is better for the necessary tests to be planned by a clinician.
Celiac disease, inflammatory bowel disease, Behçet's disease and some conditions affecting the immune system can occur together with mouth sores. Not every canker sore means a systemic disease. How often they recur and the accompanying symptoms are assessed together.
Some medicines can cause mouth ulcers or make existing sores worse. If you suspect such a link, do not stop the medicine on your own. Inform the clinician who prescribed it.
Where Do Tongue and Mouth Canker Sores Appear?
Canker sores inside the mouth are seen most often on the inner surface of the lip and cheek. The sides of the tongue, under the tongue, the floor of the mouth and the soft palate can also be affected. Blistering sores that develop on the hard palate or outside the lip may point to a different problem.
A canker sore on the tongue can be particularly uncomfortable, because it sits in an area that keeps moving while you speak and chew. The tongue rubbing against a tooth, biting the tongue and small injuries from hard foods can produce similar sores.
A sore that keeps recurring at the same spot on the tongue, or that does not heal, should not simply be regarded as a canker sore. It needs an examination for a sharp tooth edge, a broken restoration and other oral conditions.
How Do Canker Sores Heal?
Most small canker sores heal on their own. The aim of home care is not to cauterize or scrape the sore, but to reduce pain and protect the tissue from further injury. Stopping oral cleaning altogether during healing is not advised.
What Helps a Canker Sore?
- Gentle oral care with a soft-bristled toothbrush
- Eating lukewarm or cool, soft foods
- Drinking enough water to reduce dryness in the mouth
- Rinsing gently with warm salt water and spitting it out without swallowing
- Limiting foods that irritate the sore until it heals
- Asking your dentist about protective wax if an orthodontic wire is causing irritation
- Noting recurrences to follow the pattern if there is a clear trigger
Rinsing with salt water can support oral cleanliness in some people. However, if it causes burning or clear irritation, stop using it. This method should not delay the examination of a long-lasting sore.
What Should You Avoid With a Canker Sore?
- Very hot, spicy, sour and very salty foods
- Foods with hard shells or sharp edges
- Oral care products containing alcohol that sting the sore
- Squeezing, picking at the sore or poking it with a sharp object
- Crushing a painkiller tablet and placing it directly on the sore (it burns the mucosa)
- Applying lemon, garlic or strong baking soda mixtures to the sore
- Taking antibiotics or any other medicine without a clinical assessment
There are various suggestions about baking soda and different herbal applications. The evidence for these methods is limited. Strong or direct applications can irritate oral tissue and cause a chemical burn.
How Does a Dentist Assess a Canker Sore?
The dentist examines the site, size and borders of the sore and how long it has been there. You may be asked about how often you have had canker sores before, your medicines, your diet and any accompanying systemic symptoms.
Sources of irritation such as a sharp tooth, a rough filling, a denture or an orthodontic wire are checked. One situation we see often in our clinic is a sore assumed to be a canker sore that is actually caused by ongoing mechanical irritation at the same spot.
For typical, short-lived minor canker sores, laboratory tests are usually not needed. If the sores recur frequently or come with other symptoms, a clinician may consider tests such as a blood count, iron, folate and vitamin B12.
How Is Canker Sore Treatment Planned?
Treatment is planned according to the size and number of sores, the level of pain and how often they recur. The aim is to control pain, make eating easier and support the healing process.
When the dentist considers it necessary, preparations containing a topical corticosteroid, protective products or topical medicines that reduce pain can be recommended. Products that count as medicines should be used with a prescription and exactly as directed.
Antiseptic mouthwashes can be considered as supportive care in some patients. Not every mouthwash suits every mouth sore. Products containing alcohol, or used heavily, can irritate sensitive tissue further.
For numerous, large or constantly recurring canker sores, systemic treatments are planned only with a specialist assessment and a prescription. These medicines should not be self-administered for a simple, single canker sore.
When Should You See a Dentist for a Canker Sore?
Most canker sores are not caused by a serious problem. Even so, mouth sores that do not heal or that look different from your usual canker sores should be examined without delay.
- The sore shows no clear healing within two weeks, or has lasted more than three weeks
- It is larger, deeper, firmer, irregularly bordered or bleeding
- New sores appear before the old ones heal
- The sores recur at frequent intervals
- Pain makes it difficult to eat or drink
- High fever, marked fatigue or a widespread rash accompanies them
- There is redness of the eye, genital sores, or painful and swollen joints
- There is prolonged diarrhea, abdominal pain or unexplained weight loss
- Swelling in the neck or other unusual changes in the mouth are noticed
With difficulty breathing or swallowing, an inability to take fluids or rapidly increasing swelling, seek medical care without delay.
How Can Recurring Canker Sores Be Reduced?
There is no single method that completely prevents canker sores from coming back. Identifying your personal triggers and removing sources of injury inside the mouth can help reduce recurrences.
- You can record the date a sore appears, how long it lasts and what you ate beforehand.
- Sharp tooth edges and rough restorations can be checked by a dentist.
- Areas irritated by orthodontic appliances can be shown to your dentist.
- Teeth can be cleaned with a soft-bristled brush without applying too much pressure.
- Pay attention to a balanced diet, and take vitamin supplements according to test results.
- If you suspect a link, a toothpaste without sodium lauryl sulfate can be considered.
- Habits that support a regular sleep pattern and stress management can be maintained.
With recurring mouth sores, it matters to follow not only how they look but also how long they last and what symptoms come with them. A canker sore that is different from your usual ones should be assessed with an oral examination.
Frequently Asked Questions
Are canker sores contagious?
No. Canker sores are not contagious and are different from cold sores, which are caused by the herpes virus.
How many days does a canker sore take to heal?
Minor canker sores usually heal within 7–14 days. Mouth sores lasting more than three weeks, or showing no healing, should be examined by a dentist.
What causes a canker sore on the tongue?
A canker sore on the tongue can be related to biting, irritation from a sharp tooth, stress or personal triggers. A tongue sore that keeps recurring at the same spot should be examined.
Does salt water help a canker sore?
Rinsing gently with warm salt water can support oral cleanliness and reduce discomfort. If it causes burning or irritation, stop using it.
Should you take vitamins for canker sores?
Frequent canker sores can sometimes be related to an iron, folate or vitamin B12 deficiency. Supplements should be planned after a clinical assessment and the necessary tests.
How can you tell a canker sore from a cold sore?
A canker sore usually appears inside the mouth as a sore with a white-yellow center and is not contagious. A cold sore usually appears as fluid-filled blisters around the lips and can be contagious.
Should a canker sore be popped or picked?
No. Squeezing, scraping or picking at a canker sore can injure the tissue further and delay healing.