Canker Sores

Canker sores are a type of mouth sore. They’re not contagious, but they can be irritating and painful. Canker sore causes include stress, acidic foods and minor injuries to the inside of your mouth. Treatments include over-the-counter or prescription gels, ointments and rinses. Even without treatment, canker sores usually go away within two weeks.


Canker sores show up inside the mouth on the lower lip, unlike cold sores.
Canker sores show up inside the mouth on the lower lip, unlike cold sores.

What are canker sores?

Canker sores — or aphthous ulcers — are small, shallow ulcers that occur in the lining of your mouth. A canker sore starts as a white or yellowish mouth sore with a red border. They’re usually very small (less than 1 millimeter) but may grow to 1/2 inch to 1 inch in diameter.

You can get canker sores on your tongue, gums, roof of your mouth, inside of your lip or under your tongue. They can be painful and often make eating and talking uncomfortable.

There are two types of canker sores:

  • Simple canker sores: These may appear three or four times a year and last up to a week.
  • Complex canker sores: These are less common and occur more often in the people who have previously had them.

Are canker sores an STI?

No. Canker sores aren’t herpes or any other type of sexually transmitted infection (STI). In fact, they’re not contagious at all. So, you can’t spread them through kissing or sexual contact.

Canker sore vs. cold sore: Are they the same thing?

No. Although these sores are often confused for each other, they’re not the same.

Cold sores — sometimes called fever blisters — are caused by herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2). Because cold sores are caused by viruses, they’re highly contagious and can spread through close personal contact, such as kissing or oral sex. Cold sores are fluid-filled blisters, and they can appear in clusters on your mouth or genitals.

Canker sores, on the other hand, aren’t caused by an infection and aren’t contagious.

Who gets canker sores?

Anybody can develop canker sores. But they’re most common in teens and people in their 20s. Women and people assigned female at birth (AFAB) are more likely than men and people assigned male at birth (AMAB) to get canker sores. Experts believe this could be due to hormonal changes.

How common is this condition?

Canker sores are fairly common. Approximately 20% of the U.S. population has had a canker sore at least once in their lifetime.


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Symptoms and Causes

What are the symptoms of canker sores?

Common canker sore symptoms include:

  • One or more painful sores inside of your mouth. These ulcers may form on your tongue, the inside of your lips, your inner cheeks or the roof of your mouth.
  • Burning or tingling sensations.
  • Small, round ulcers that are white, gray or yellow with a red border.

In severe cases, you may also experience:

What causes canker sores?

Experts aren’t exactly sure why some people are more likely to get canker sores. But they’ve discovered many factors that can trigger the development of these ulcers, including:

Complex canker sores may develop in people with immune system conditions, including:

Canker sores may also be linked to nutritional deficiencies in vitamin B-12, zinc, folic acid or iron.


Are canker sores contagious?

No. Canker sores aren’t contagious because they’re not caused by an infection.

Diagnosis and Tests

How are canker sores diagnosed?

Your healthcare provider can diagnose canker sores during a physical exam. They might also recommend a blood test to see if you have a vitamin deficiency or another condition that’s causing the ulcers.


Management and Treatment

How do you heal a canker sore fast?

Canker sore treatment may include over-the-counter or prescription products to ease your symptoms. Your healthcare provider may recommend one or more of these canker sore remedies:

If you have canker sores caused by nutritional deficiencies, your healthcare provider may recommend certain vitamins or supplements.

For severe canker sores, your healthcare provider may recommend cauterization (burning the affected tissue). This can sterilize the area, reduce pain and speed up healing.

How long do canker sores last?

Canker sore pain usually improves in a few days and the ulcers typically heal within two weeks, even without treatment. If you have a canker sore that lasts for more than two weeks, schedule an appointment with your healthcare provider.


Can I prevent canker sores?

There’s no surefire way to prevent canker sores. But there are several things you can do to reduce your risk:

  • Steer clear of acidic, salty or spicy foods.
  • Practice good oral hygiene. Brush twice a day with a soft-bristled toothbrush and floss once daily.
  • Talk to your healthcare provider about potential nutritional deficiencies.

Try stress reduction techniques, such as mindfulness and meditation.

Outlook / Prognosis

What can I expect if I have a canker sore?

If you develop a canker sore, there are several over-the-counter treatments that can manage your symptoms, including rinses and topical ointments.

If you have canker sores that are unusually large, or if your symptoms interfere with your daily life, schedule a visit with your healthcare provider.

Living With

When should I see my healthcare provider?

You should call your healthcare provider if you have canker sores that:

  • Begin to spread.
  • Are unusually large.
  • Last longer than two weeks.
  • Interfere with eating, drinking or other daily routines.
  • Are accompanied by a high fever.

What questions should I ask my healthcare provider?

If you’ve scheduled an appointment with your healthcare provider, here are some questions you may want to ask:

  • Is my mouth ulcer a canker sore?
  • What could have caused it?
  • Will you need to run tests?
  • What are my treatment options?
  • How can I manage my symptoms at home?
  • How long until my canker sore goes away?
  • Are there ways to reduce my risk for canker sores in the future?

A note from Cleveland Clinic

Canker sores can be irritating, and they’re certainly inconvenient, but they’re not dangerous. Unlike cold sores, canker sores aren’t caused by infections and can’t be spread from person to person. Most people find relief by using over-the-counter canker sore treatments. But if your symptoms don’t improve after trying these products, you should talk to your healthcare provider. They can tell you how to get rid of canker sores so you can get back to normal life.

Medically Reviewed

Last reviewed on 06/09/2022.

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