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What Is a Canker Sore?

A canker sore is a small, shallow open wound (or ulcer) in your mouth that can make eating and talking uncomfortable. They’re also known as aphthous ulcers. There are a few types of canker sores:

  • Minor canker sores. These may show up three or four times a year. They typically happen in people ages 10 to 20. They’re less than 1 centimetre across and heal in about a week with no scarring.
  • Major canker sores. These are less common. The ulcers are bigger and can last more than 2 weeks. They often heal with scarring.
  • Herpetiform canker sores. These are rare and show up as clusters of tiny ulcers. They usually heal in about a week.

Burning or tingling spot in your mouth? A canker sore may be on the way. They are not contagious and you can have more than one at a time. Common causes are acidic foods, spicy foods, skin that’s already irritated, and being on your menstrual cycle. Canker sores mostly heal on their own and don’t leave a scar. Some over-the-counter medicines may soothe the area. If it’s not better in 2 weeks, call your doctor.

Canker Sore Causes and Risk Factors

Doctors don’t know what exactly causes most canker sores.

Things that might cause minor sores include:

  • Stress
  • Tissue injuries. Examples being a sharp tooth or a dental appliance
  • Certain foods, including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes, and strawberries)
  • Nonsteroidal anti-inflammatory drugs like ibuprofen
  • An allergy to something in your food or in your toothpaste or mouthwash
  • Helicobacter pylori, the bacteria that can cause peptic ulcers

Things that might cause complex canker sores include:

  • An underlying health condition like a weakened immune system, HIV/AIDS, lupus, or Behcet’s disease
  • Nutritional problems like too little vitamin B12, zinc, folic acid, or iron
  • Gastrointestinal diseases like celiac or Crohn’s

About 1 in 5 people develop canker sores regularly. They’re more common in women, possibly because of hormonal differences. They may also run in families.

Canker Sore vs. Cold Sore

Canker and cold sores are not the same.

Cold sores, also called fever blisters or herpes simplex type 1, are groups of painful, fluid-filled blisters. Unlike canker sores, a virus causes cold sores, and they’re highly contagious. Also, cold sores typically appear outside your mouth — usually under your nose, around your lips, or under your chin — but canker sores show up inside your mouth.

Canker Sore Symptoms

You may have a canker sore if you have:

  • A painful sore or sores inside your mouth: on your tongue, on your soft palate (the back portion of the roof of your mouth), or inside your cheeks
  • A tingling or burning sensation before the sores appear
  • Sores in your mouth that are round, white or gray, with a red edge or border

Severe canker sore attacks may also cause:

  • Fever
  • Fatigue
  • Swollen lymph nodes

Canker Sore Diagnosis

Canker sores usually aren’t serious. Call your dentist if you have:

  • Unusually large sores
  • Sores that spread
  • Sores that last 3 weeks or longer
  • Extreme pain despite avoiding trigger foods and taking over-the-counter pain medication
  • Trouble drinking enough fluids
  • High fever with canker sores

Your dentist can usually make a diagnosis based on a physical exam and your medical history.

Canker Sore Treatment

Pain from a canker sore tends to get better in a few days, and the sores usually heal without treatment in about a week or two. Treatment for large, long-lasting, or unusually painful sores might include:

  • Mouthwashes. Your doctor can prescribe a rinse that has a steroid or a painkiller.
  • Oral medications.
  • Nutritional supplements. You might need these if a nutrient deficiency is causing your canker sores.
  • Cautery. Dental lasers can help you feel better right away. Your doctor can also cauterize sores with chemicals like debacterol or silver nitrate.

Canker Sore Home Remedies

Home treatments to speed healing and help you feel better include:

  • Topical products. Medicated gels, creams, pastes, and liquids go on the sore.
  • Mouth rinses. Mix salt or baking soda in warm water, and swish it around your mouth.
  • Milk of magnesia. Put a bit on a cotton swab, and dab it on the sore.

Canker Sore Prevention

There is no cure for canker sores, and they often come back. But you might get them less often if you:

  • Avoid foods that irritate your mouth, including citrus fruits, acidic vegetables, and spicy foods
  • Avoid chewing gum
  • Brush your teeth with a soft-bristled brush after meals, and floss daily, which will keep your mouth free of foods that might trigger a sore
Medical Reference Reviewed by Jennifer Robinson, MD on November 19, 2019




Cleveland Clinic: “Canker Sores.”

American Academy of Oral Medicine: “Canker Sores.”

Mayo Clinic: “Canker sore.”

Nemours/TeensHealth: “Canker Sores.”