Canker Sores

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What are canker sores?

Canker sore is the name for a painful, open sore in the mouth that is medically known as aphthous ulcer. The sores are not contagious and are small, shallow lesions that develop on the soft tissues in the mouth and gums.

Canker sores are more common in women than men. Most commonly, canker sores first appear between the ages of 10 and 40. Canker sores may result from mouth injury, viral infections, hormonal shifts, an abnormal immune system, or a diet low in nutrients.

Signs and symptoms of canker sores can last for about one week. The disease course varies among individuals. Some people with canker sores have one painful red spot that develops into an open ulcer that is usually white or yellow, while others may have swollen lymph nodes, fever, and more than one canker sore at a time. Fortunately, you can treat canker sores successfully with over-the-counter remedies to reduce pain. Even better, you can reduce your risk of canker sores by carefully brushing your teeth so as not to injure your mouth, eating a nutritious diet, and reducing stress.

Seek immediate medical care (call 911) for serious symptoms such as high fever (higher than 101 degrees Fahrenheit) and difficulty swallowing or breathing.

Seek prompt medical care if you are being treated for canker sores but mild symptoms recur or are persistent.


What are the symptoms of canker sores?

Canker sores cause a local area of inflammation in the mouth that may result in a number of symptoms. The symptoms can vary in intensity among individuals.

Common symptoms of canker sores

The most common symptoms of canker sores are found in the mouth and include:

  • Pain
  • Red spot or bump that develops into an open ulcer
  • Single bump or group of bumps
  • Sore that heals without scarring in one to two weeks
  • White or yellow center ulcer

Less common symptoms of canker sores

Less common symptoms of canker sores are related to a more severe form and include:

  • Clusters of sores
  • Extensive scarring
  • Fever
  • Listlessness
  • Sore greater than 0.5 inch, or 12 mm, in diameter
  • Sore with irregular edges
  • Swollen lymph nodes

Symptoms that might indicate a serious condition

In some cases, canker sores can be a serious condition that should be evaluated immediately in an emergency setting. Seek prompt medical care if you, or someone you are with, have any of these serious symptoms including:


What causes canker sores?

A variety of factors can cause canker sores, including injury during tooth brushing, dental work, trauma or emotional stress, hormonal changes, spicy foods, and nutrient deficiencies. The sores occur commonly with viral infections. In some cases, the cause cannot be identified.

Common causes of canker sores

It is not always possible to determine what caused a canker sore. The most common causes of canker sore include:

  • Hormonal changes

  • Minor injuries during tooth brushing or dental work

  • Nutritional deficiencies

  • Spicy foods

  • Stress

  • Toothpastes and mouth rinses containing sodium lauryl sulfate

  • Viral infections

Disease causes of canker sores

Canker sores can also be associated with certain diseases including:

What are the risk factors for canker sores?

A number of factors increase the risk of developing canker sores. Not all people with risk factors will get canker sores. Risk factors for canker sores include:

  • Abnormal immune system

  • Biting your cheek or tongue

  • Family history

  • Food allergies

  • Hormonal changes

  • Mouth injury


How are canker sores treated?

Treatment for canker sores does not normally require medical care from your health care provider unless the symptoms cause you concern or are persistent. If you experience more than three canker sores in one year you should contact your health care provider.

Over-the-counter anesthetics and antimicrobial mouth rinses are the mainstay of treatment for canker sores and can be highly effective. If you receive medical care, it is important to follow your treatment plan for canker sores precisely and to follow instructions carefully to enhance recovery.

Treatments for canker sores

Preparations that are effective in the treatment of canker sores include:

  • Baking soda paste

  • Mouth rinses, such as salt water, baking soda (dissolve 1 teaspoon of soda in 1/2 cup warm water), hydrogen peroxide diluted by half with water, or a mixture of 1 part diphenhydramine (Benadryl) to either 1 part bismuth subsalicylate (Kaopectate) or 1 part simethicone (Maalox)

  • Milk of magnesia placed directly on the canker sore

  • Numbing agents, such as benzocaine (Anbesol, Orajel), ice, or ice chips

What you can do to improve your canker sores

In addition to following your health care provider’s instructions and taking all medications as prescribed, you can speed your recovery by:

  • Avoiding hot, spicy or acidic foods that can irritate the sore

  • Brushing teeth gently, using a soft brush

  • Placing oral bandages on ulcers

  • Seeing your dentist if the sores do not heal or are painful

What are the potential complications of canker sores?

You can help minimize your risk of serious complications by following the treatment plan you and your health care professional design specifically for you. Complications of canker sores include:

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2019 Jan 4
  1. Canker sores. PubMed Health, a service of the NLM from the NIH.
  2. Canker sores, cold sores and common mouth sores. ADA: American Dental Association.
  3. Domino FJ (Ed.) Five Minute Clinical Consult. Philadelphia: Lippincott Williams & Wilkins, 2013.
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