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Your guide to canker sores

Canker sores, also called aphthous ulcers, are small sores that form inside of the mouth. They commonly appear inside the cheeks, lips, on or under the tongue, the roof of the mouth and on the gums.

Canker sores are usually white or yellow and sometimes have a small red border surrounding them. Early symptoms of a canker sore can be a small bump or red spot that produces a slight burning or tingling sensation.

Canker sore or cold sore?

Canker sores are not the same as cold sores. Cold sores (also known as fever blisters) are caused by the herpes simplex virus and are contagious. Canker sores, on the other hand, appear on their own and can't be spread to other people.

When you're trying to figure out whether you have a canker sore or a cold sore, check if the sore is inside or outside the mouth. If it's inside your mouth, it's most likely a canker sore; outside, probably a cold sore. A tingling feeling can also indicate a cold sore.

Both canker sores and cold sores can be triggered by stress and lack of sleep.

What causes a canker sore?

Canker sores can be caused by trauma such as biting your cheek, jabbing your gum with your toothbrush or even overzealous tooth cleaning.

Other causes of canker sores include:

  • Braces, retainers or dentures rubbing against your cheek
  • Genetics
  • Fatigue
  • Stress
  • Weakened immune system
  • Chemotherapy
  • Nutritional problems or deficiencies
  • Menstruation
  • Spicy foods
  • Irritants in toothpaste

How to treat a canker sore

Canker sores can be quite painful, especially when talking or eating. To minimize the pain, avoid the following:

While there is no cure for canker sores, there are some treatments that you can try to ease the discomfort until the sores go away on their own:

  • Over-the-counter pain medication (such as aspirin or ibuprofen) for general pain relief
  • Over-the-counter topical anesthetic, including some gels or patches that form a protective covering for the sore
  • Aloe vera juice

Canker sores usually disappear in about seven to 10 days. If your sore doesn’t heal after two weeks, you should see your dentist to rule out other causes, such as oral cancer.

Related reading:

Last updated: June 2018

The oral health information on this website is intended for educational purposes only. You should always consult a licensed dentist or other qualified health care professional for any questions concerning your oral health.