Canker sores, also known as aphthous ulcers or aphthous stomatitis, are small pitted lesions (sores) that occur inside of the mouth. The exact cause is unknown, but they are not contagious.

Roughly 20% of people will develop canker sores at some time in their life. Canker sores only occur inside the mouth and should not to confused with cold sores caused by the herpes simplex virus.

We tend to think of canker sores as one thing, but there are actually different types with different features and risk factors.

This article describes the three types of canker sores—including their appearance and who they most commonly affect—as well as the underlying causes, symptoms, and treatments.

Types of Canker Sores

Not all canker sores are alike. Canker sores may be classified as minor, major, or herpetiform.

Minor

Minor canker sores are the most common type accounting for around 80% of cases. The size can vary, but they are typically between 1/3 inch and 1/2 inch. They are also sometimes referred to as simple canker sores.

Although painful, minor canker sores are often fully healed within two weeks. They can occur spontaneously, often after a minor mouth injury or during times when you are chronically overworked and exhausted.

Major

Major canker sores larger than 1/2 inch tend to last more than two weeks. Where minor canker sores are typically round and symmetrical, major canker sores often have irregular, oddly-shaped borders. On rare occasions, this type of canker sore can leave behind a scar.

Major canker sores are common in people who are immunosuppressed due to chemotherapy or conditions like HIV. Major canker sores may also be referred to as complex canker sores. These account for 15% of canker sores.

Herpetiform Canker Sores

Herpetiform canker sores are a cluster of several tiny lesions that often converge to form one large sore. Hundreds of pinhead-sized lesions can be involved. Herpetiform canker sores may last from one week to one month.

Click Play to Learn About the Potential Causes of Canker Sores

This video has been medically reviewed by Brian T. Luong, DMD

Herpetiform canker sores can look like a herpes outbreak, but the herpes virus is not involved. The cause is unknown but they tend to occur later in life.

Herpetiform canker sores represent 5% of aphthous ulcer diagnoses.

Canker Sore Symptoms

Canker sores appear inside of the mouth as round or oval sores typically with a raised border and a yellow, gray, or white center. Canker sores typically develop:

Recap

Minor canker sores, which are smaller and round, are the most common type. Major canker sores are larger and irregular and more commonly seen in immunocompromised people. Herpetiform cankers sores cause clusters of pinhead-sized lesions, mainly in older people.

  • On the top surface of the tongue and the tip of the tongueUnderneath the tongue and on the floor of the mouthOn the inside of the cheek or lipOn the gum tissue

One to two days before the appearance of the lesion, there may be a localized burning or tingling sensation inside the mouth.

Canker sores can become quite painful, especially when eating, drinking, and talking.

Causes

While we don’t know exactly what causes canker sores, several risk factors have been identified. These include:

Canker sores are most often round with raised edges and lighter centers. They are typically painful and most often occur on the inner lip, cheek, or gums as well as on or under the tongue.

  • A minor mouth injury (such as a dental injury, biting your cheek, or wearing poorly fitting dentures)
  • Food sensitivities (particularly to coffee, chocolate, strawberries, and spicy and acidic foods)
  • Vitamin deficiency (particularly vitamin B-12, folate, iron, and zinc)
  • Hormonal changes during menstruation
  • Celiac disease
  • Inflammatory bowel disease (IBD)
  • Immunodeficiency disorders like HIV
  • Helicobacter pylori (the bacteria that causes peptic ulcers)
  • Emotional stress

Treatment

Canker sores do not necessarily need to be treated. If they do, they may respond to at-home remedies like a saltwater-and-sodium-bicarbonate mouth rinse. Over-the-counter options include topical numbing agents like Anbesol (benzocaine) and antiseptic mouthwashes containing hydrogen peroxide.

There are numerous risk factors associated with cankers sores including mouth injuries, food sensitivities, stress, menstruation, vitamin deficiencies, digestive disorders or infections, and impaired immunity.

When severe, prescription drugs may be needed. These include topical steroids like Lidex (fluocinonide), antacids like Carafate (sucralfate), or oral steroids like Decadron (dexamethasone).

One of the best ways to avoid canker sores is to treat the underlying cause. Improperly fitting dentures or broken teeth should be repaired. Dietary changes may help if you have celiac disease or IBD or tend to get sores after eating certain foods.

Stress management techniques may also help as stress appears to trigger canker sores in some people.

Summary

Canker sores, also known as aphthous ulcers, are painful, pitted sores inside the mouth. There are three different types: minor canker sores (the most common type), major canker sores (often seen in immunosuppressed people), and herpetiform canker sores (which cause clusters of pinhead-sized lesions).

Canker sores do not always need to be treated. Depending on their severity and suspected, the treatment may involve antiseptic mouthwash, numbing agents, prescription antacids, topical or oral steroids, changes in diet, and stress reduction.

Although the cause of canker sores is poorly understood, they are linked to stress, mouth injuries, food sensitivities, vitamin deficiency, menstruation, digestive disorders, and impaired immunity. Canker sores don’t always need to be treated, but some may benefit from a topical numbing agent, antiseptic mouthwash, changes in diets, and oral or topical steroids.

A Word From Verywell

Canker sores can be uncomfortable and make it difficult to eat, or even talk. Most of the time canker sores do not need to be treated. But you may want to seek treatment from a dentist or doctor if you have recurrent sores or your canker sores fail to heal after 14 days.

Frequently Asked Questions

  • How do you treat a major canker sore?
  • If your canker sore is large and painful, your healthcare provider may prescribe an antibacterial mouth rinse or a corticosteroid ointment. Over-the-counter oral pain gels are also available to help ease symptoms.
  • How long does it take a major canker sore to heal?
  • Major canker sores can take between four and six weeks to heal. Severe sores may also leave a scar.

If your canker sore is large and painful, your healthcare provider may prescribe an antibacterial mouth rinse or a corticosteroid ointment. Over-the-counter oral pain gels are also available to help ease symptoms.

Major canker sores can take between four and six weeks to heal. Severe sores may also leave a scar.