Medically Reviewed by Brunilda Nazario, MD on May 27, 2021

What Are Canker Sores?

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Canker sores (you might hear your doctor call them aphthous ulcers) are small sores that pop up on the soft tissues inside your mouth or on your gums. They can hurt, which can make talking or eating harder than usual. After about a week or two, most canker sores will go away on their own. They're pretty common. About 1 in 5 people get them regularly.

Canker Sore Symptoms

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Canker sores are usually oval or circular. They’re mostly yellow or white with a red border. You’ll find them somewhere in your mouth, like inside your cheeks or around your gums and tongue. They can even pop up on the roof of your mouth. A few days before a canker sore shows up, you might have a burning or tingling feeling.  

During a more serious canker sore attack, you might feel sluggish and have a fever or swollen lymph nodes.

Are Canker Sores the Same as Cold Sores?

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They aren't. Cold sores are blisters that have liquid inside them. Although they can both hurt, canker sores don’t appear on your lips, chin, or nostrils like a cold sore does. Canker sores aren't caused by viruses like cold sores are. So you can’t spread canker sores like you can spread cold sores. And you can’t get canker sores from kissing or from sharing food.

Minor Canker Sores

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There are a few types of canker sores. Minor canker sores are the most common. If you have one, it’ll probably be small and shaped like an oval with a red border. It'll also heal in a week or two.

Major Canker Sores

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These aren’t as common. They'll usually be bigger, deeper, and circular with a clear border. If they're really big, they could have jagged edges, too. Major canker sores are very painful. They also take longer to heal -- as long as 6 weeks -- and they may give you a scar.

Herpetiform Canker Sores

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These usually pop up later in life. If you have herpetiform canker sores, that doesn’t mean you have herpes. The herpes virus doesn't cause them. These will usually be about the size of a pinpoint with jagged edges. They also form in clusters of 10-100 sores (but they could make up one very big sore), and they usually heal in a week or two.

Causes of Canker Sores

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Doctors don’t really know what causes canker sores. They think a combination of things can bring outbreaks.

Some of those things include:

  • Certain mouthwashes or toothpastes
  • Dental work or brushing your teeth too much or too hard
  • Food sensitivities
  • Hormonal shifts during your period
  • Not getting enough folate (also called folic acid), iron, vitamin B12, or zinc
  • Stress
  • Anti-inflammatory drugs like ibuprofen

Conditions That Cause Canker Sores

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If you have a canker sore, it could also be because of a disease or condition, like:

  • Behcet’s disease, a rare condition that encourages inflammation in your body, especially your blood vessels
  • Celiac disease, a serious condition that happens because your body is sensitive to gluten (a protein that lots of grains have)
  • Inflammatory bowel diseases, like ulcerative colitis or Crohn’s disease
  • Lupus, a condition where your immune system attacks your body’s tissues
  • HIV or AIDS, both of which can overpower your immune system

Who Gets Canker Sores?

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Anyone can get a canker sore. They’re usually more common in young adults or teenagers, and women get them more often than men. If you get them a lot, you might have a family history of them. This can happen because of your genes or because of something in your environment (like the foods you eat or allergens around you).

Canker Sore Home Remedies

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Some things you can do at home can speed up healing and ease the pain. You can:

  • Avoid acidic or spicy foods.
  • Brush your teeth gently.
  • Put ice on your canker sore.
  • Putting a dab of magnesium hydroxide on your sore a couple of times per day.
  • Rinse your mouth with saltwater or a mix of baking soda and water. (Mix 1 teaspoon of baking soda in half a cup of warm water.)

Canker Sore Treatments

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If you have a minor canker sore, you probably won’t need treatment since the sores go away on their own in a week or so. But if you have big, painful sores that don’t go away, there are lots of things your doctor can prescribe that can help. These include topical medications, mouthwashes, nutritional supplements, or cautery -- a chemical to burn the area where you have a sore. There are also creams, gels, liquids, and pastes that you get by prescription or over the counter.

Can You Prevent Canker Sores?

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If you get canker sores, there’s a chance you’ll get them again. But you can lower your odds by eating a healthy diet, watching your stress, and practicing good oral health habits. If you have dental appliances like braces, talk to your dentist about special dental wax to cover sharp edges.

When to See a Doctor

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Check in with yours if you have:

  • Really big canker sores
  • Sores that keep coming back or new sores that pop up before the old ones heal
  • Pain that doesn’t go away
  • A hard time drinking or eating
  • Sores that last 2 weeks or more
  • A high fever with your canker sores
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