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Mouth Sores: At a Glance

By The Manual's Editorial Staff, ,

Mouth sores are holes that form in the lining of the mouth (ulcers) when the top layer of cells breaks down. Mouth sores vary in appearance and size and can affect any part of the mouth, including the lips, tongue, floor of the mouth, and soft palate.

A View of the Mouth

Many mouth sores appear red, but some are white because of dead cells and food debris inside the center portion. Some sores are raised and filled with fluid, similar to blisters.

For a full discussion, see Mouth Sores and Inflammation.

What Causes Mouth Sores?

There are many causes of mouth sores.

The most common specific causes of mouth sores are

  • Viral infections (particularly herpes simplex and herpes zoster)

  • Other infections (caused by fungi or bacteria)

  • Injury (such as lip-biting)

  • Irritating food or other substances (such as certain ingredients in some toothpastes and mouthwashes)

  • Tobacco use

  • Drugs (particularly chemotherapy drugs) and radiation therapy

  • Systemic disorders (such as Behçet disease and Stevens-Johnson syndrome)

Rarely, a mouth sore is a cancer or is precancerous. Precancerous means that if untreated, it may progress to cancer, sometimes after years.

Warning Signs for People With Mouth Sores

In people with mouth sores, certain symptoms and characteristics are cause for concern because they may be signs of a systemic disorder. Warning signs include

  • Fever

  • Blisters on the skin

  • Inflammation of the eye

  • Any sores in people with a weakened immune system (such as people with HIV infection)

Did You Know...

  • All people with a sore that lasts for 10 days or more must be examined by a dentist or doctor to determine whether the sore is cancerous, precancerous, or not.

People who have warning signs should see a doctor right away. People who have no warning signs but have a lot of pain, feel generally ill, and/or have trouble eating should see a doctor within several days.

How Are Mouth Sores Treated?

Strategies can include

  • Treating the disorder (such as an infection) that is causing the mouth sores

  • Avoiding any substances or drugs that are causing the sores

  • Applying an anesthetic (such as lidocaine) or other treatment (such as a corticosteroid) directly to the sores as directed by a doctor or dentist

  • Occasionally, being treated with a laser, which relieves pain immediately and often prevents sores from returning

If the cause is cancer, surgery is required.

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