A canker sore, or aphthous ulcer, is a type of mouth ulcer. They can cause local pain and other symptoms. In most cases, a canker sore will heal naturally without medical treatment.

Although they can be very uncomfortable, they are rarely a cause for concern.

In this article, we ask if there is anything that can be done to relieve canker sores, and if there are times when they require medical attention.

Fast facts on canker sores

  • Although there are known risk factors, the causes of canker sores are still not known.
  • Most canker sores do not need medical attention and can be treated at home.
  • Canker sores typically heal naturally, within 2 weeks.
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Canker sores, also known as aphthous ulcers, are a common oral health complaint.

A canker sore is a type of mouth ulcer, known medically as an aphthous ulcer. Canker sores are one of the most common complaints of the mouth.

They can occur at any age but are more likely in younger adults and women.

Children as young as 2 years may develop canker sores, but they do not normally appear until adolescence.

Although most people only have occasional canker sores, around 20-30 percent of people have recurrent episodes.

Canker sores are sometimes split into two categories:

Simple canker sores: they appear 3-4 times a year; they generally occur in people aged 10-20, and last about 1 week.

Complex canker sores: less common, larger, and more painful. They may last up to 1 month and leave a scar. Complex canker sores are often due to an underlying condition, such as a compromised immune system, Crohn’s disease, or vitamin deficiency.

Researchers have not yet provided a scientific explanation of why canker sores develop; however, there are some factors that are known to be involved, including viral infection.

The causes of recurrent cases of canker sore – known as recurrent oral aphthous ulcers or recurrent aphthous stomatitis – are also unclear, although there are links with a number of factors including a family history of aphthous ulcers, and allergies.

Ulcers are sometimes associated with other conditions needing medical attention, such as inflammatory bowel disease, compromised immunity, allergies, and nutritional deficiency.

The following factors are thought to be involved in the development of canker sores:

  • Hormonal changes.
  • Physical trauma (damage to the lining of the mouth, such as during dental treatment).
  • Drugs.
  • Food hypersensitivity – for instance, citrus fruits and tomatoes can trigger or worsen a canker sore.
  • Nutritional deficiencies, including iron, folic acid, zinc, and vitamin B12.
  • Stress.

A report by the United States Surgeon General estimates that up to 25 percent of the general population are affected by recurrent canker sores, noting there may be higher numbers among selected groups, such as health professional students.

Canker sores cause local pain and can be easily irritated. In simple cases, these are the only symptoms, although the pain may cause feelings of being fed up with the mouth ulcer.

Common features of canker sores include:

  • Well-defined, round, smaller than a centimeter across, and usually shallow in the mouth’s lining – mucosal surface.
  • Sometimes there is a tingling sensation before they appear.
  • White or yellow-gray center surrounded by an inflammatory red margin.
  • Often fading to gray over time.
  • Normally in the front part of the mouth, on its floor, inside of the lip (labial mouth), inside of the cheeks (buccal), or under the front or sides of the tongue.
  • Sometimes affecting the gums and, relatively uncommonly, the surface of the back part of the mouth.
  • Typically persists for 1-2 weeks before healing.

In some, more severe cases, symptoms can include:

  • feeling sluggish
  • swollen lymph nodes
  • fever

Canker sores and cold sores are different conditions:

  • Canker sores appear as white circles with a red halo; cold sores are normally fluid-filled blisters.
  • Canker sores appear inside the mouth; cold sores appear outside the mouth- often under the nose, around the lips, or under the chin.
  • Canker sores are not contagious; cold sores are caused by the herpes simplex virus (HSV) and, more rarely, HSV-2 (the genital herpes virus). Cold sores are contagious.
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If canker sores persist without improvement for more than 2 weeks, a doctor should be consulted.

Common canker sores usually heal without the need for medical treatment. More severe or recurrent cases may be eased by prescribed treatments, although these do not “cure” the ulcers.

As a general guide, canker sores should be brought to the attention of a dentist or doctor when they:

  • Persist for more than 2 weeks without improvement.
  • Get worse – including while being treated with home remedies.
  • Recur often (2-3 times a year or more) or are particularly numerous or severe.
  • Are accompanied by other symptoms, such as fever, diarrhea, headache, or skin rash.
  • Are thought to be part of another condition.

The good news is that the pain and discomfort of canker sores can be reduced by readily available prescription and non-prescription treatments and home remedies.

Simple cases of occasional canker sores are self-limiting; they will heal over and disappear without intervention. No remedies are proven to change the course of canker sores themselves or stop them returning – treatments mostly just reduce pain, discomfort, and complication.

Few treatments marketed for canker sores have been through extensive clinical testing.

The management of canker sores is focused on treating symptoms, reducing inflammation, and promoting the healing process by countering secondary effects that could slow this down, such as bacterial infection.

Treatments may include steroid mouth rinses, topical anesthetics, antiseptic ointments/rinses, or nutritional supplements.

Home remedies for canker sores

The home remedy below is suggested by the U.S. Library of Medicine and can be followed three or four times a day:

  • Rinse with mild, over-the-counter mouthwash or salt water (do not swallow).
  • Make a mixture that is half hydrogen peroxide and half water.
  • Use a cotton swab to apply some of the mixture directly to the sore.
  • Dab a small amount of milk of magnesia on the sore.

So-called alternative therapies may also be worth trying. A review of the management of canker sores written for the journal American Family Physician, listed a number of options, although it noted that there had been no randomized controlled trials to properly test safety and efficacy:

  • Anecdotes of relief and better healing from sucking on zinc gluconate lozenges (sold for the common cold).
  • Vitamin C, vitamin B complex, and lysine “may speed healing when taken orally at the onset of lesions.”
  • Sage and chamomile mouthwash 4-6 times a day may help – infuse equal parts of the two herbs in water.
  • Carrot, celery, and cantaloupe juices “have been reported as helpful.”

Prescription therapies for canker sores

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A doctor may prescribe antibiotics to minimise inflammatory irritation.

More severe or persistent cases of canker sores need to be checked by a doctor to rule out associated conditions or to access prescription treatments.

Again, any treatments aimed at the ulcers themselves are not certain to change their course, but can ease the symptoms.

Antibiotics may be prescribed to minimize inflammatory irritation whether or not a bacterial infection is present.

Anesthetics, as well as being available in consumer products for canker sores, may also be prescribed as topical preparations to ease irritation and pain.

Some medicines designed for other conditions can sometimes be used. The American Academy of Oral & Maxillofacial Pathology, for example, cites an association between recurrent cases of canker sores and an overactive immune system, so topical immunosuppressant medications may help, such as locally applied cortisone.

With a similar mode of action, topical corticosteroids are often considered by doctors; these include clobetasol ointment, dexamethasone rinse, and fluocinonide gel (Lidex). One possible side effect of using corticosteroids against canker sores is a fungal infection in the mouth.

Particularly severe or recurrent cases of canker sores may be referred to an oral specialist who might consider systemic rather than locally applied (topical) drugs.

These specialists may also be needed to make a more specific diagnosis – some rare cases of recurrent canker sores are diagnosed as Sutton disease, for example.

The question of what can be done to prevent canker sores in the first place has no clear answer. However, there are ways to prevent canker sores from getting or feeling worse.

Prevent aggravation of canker sores by avoiding:

  • Abrasive foods or those that can stick in the mouth (potato chips, for example).
  • Spicy, acidic, or hot foods and drinks.
  • Traumatizing the ulcers (through harsh contact with toothbrush bristles, for example).