What causes mouth ulcers? 25 possible conditions

Mouth ulcers — also known as canker sores — are normally small, painful lesions that develop in your mouth or at the base of your gums. They can make eating, drinking, and talking uncomfortable. Women (more than men), adolescents, and people with a family history of mouth ulcers are at higher risk for developing mouth ulcers.

Mouth ulcers aren’t contagious and usually go away within one to two weeks. However, if you get a canker sore that is large or extremely painful or if it lasts for a long time without healing, you should seek the advice of a doctor.

What Triggers Mouth Ulcers?

There is no definite cause behind mouth ulcers. However, certain factors and triggers have been identified. These include:

  • minor mouth injury from dental work, hard brushing, sports injury, or accidental bite
  • toothpastes and mouth rinses that contain sodium lauryl sulfate
  • food sensitivities to acidic foods like strawberries, citrus, and pineapples, and other trigger foods like chocolate and coffee
  • lack of essential vitamins, especially B-12, zinc, folate, and iron
  • allergic response to mouth bacteria
  • dental braces
  • hormonal changes during menstruation
  • emotional stress or lack of sleep
  • bacterial, viral, or fungal infections

Mouth ulcers also can be a sign of conditions that are more serious and require medical treatment, such as:

  • celiac disease (a condition in which the body is unable to tolerate gluten)
  • inflammatory bowel disease
  • diabetes mellitus
  • Bechet’s disease (a condition that causes inflammation throughout the body)
  • a malfunctioning immune system that causes your body to attack the healthy mouth cells instead of viruses and bacteria
  • HIV/AIDs

What Symptoms Are Associated with Mouth Ulcers?

There are three types of canker sores: minor, major, and herpetiform.


Minor canker sores are small oval or round ulcers that heal within one to two weeks with no scarring.


Major canker sores are larger and deeper than minor ones. They have irregular edges and can take up to six weeks to heal. Major mouth ulcers can result in long-term scarring.


Herpetiform canker sores are pinpoint size, occur in clusters of 10 to 100, and often affect adults. This type of mouth ulcer has irregular edges and will often heal without scarring within one to two weeks.

You should see a doctor if you develop any of the following:

  • unusually large mouth ulcers
  • new mouth ulcers before the old ones heal
  • sores that persist more than three weeks
  • sores that are painless
  • mouth ulcers that extend to the lips
  • pain that can’t be controlled with over-the-counter or natural medication
  • severe problems eating and drinking
  • high fever or diarrhea whenever the canker sores appear

How Are Mouth Ulcers Diagnosed?

Your doctor will be able to diagnose mouth ulcers through a visual exam. If you’re having frequent, severe mouth ulcers, you might be tested for other medical conditions.

What Are Some Ways to Treat Mouth Ulcers?

Most mouth ulcers don’t need treatment. However, if you get mouth ulcers often or they’re extremely painful, a number of treatments can decrease pain and healing time. These include:

  • using a rinse of saltwater and baking soda
  • placing milk of magnesia on the mouth ulcer
  • covering mouth ulcers with baking soda paste
  • using over-the-counter benzocaine (topical anesthetic) products like Orajel or Anbesol
  • applying ice to canker sores
  • using mouth rinse that contains a steroid to reduce pain and swelling
  • using topical pastes
  • placing damp tea bags on your mouth ulcer
  • taking nutritional supplements like folic acid, vitamin B6, vitamin B12, and zinc
  • trying natural remedies such as chamomile tea, echinacea, myrrh, and licorice

Tips to Prevent Mouth Ulcers

You can take steps to reduce the occurrence of mouth ulcers. Avoiding foods that irritate your mouth can be helpful. That includes acidic fruits like pineapple, grapefruit, oranges, or lemon, as well as nuts, chips, or anything spicy. Instead, choose whole grains and alkaline (nonacidic) fruits and vegetables. Eat a healthy, well-balanced diet and take a daily multi-vitamin.

Try to avoid talking while you’re chewing your food to reduce accidental bites. Reducing stress and maintaining good oral hygiene by using dental floss daily and brushing after meals also may help. Finally, get adequate sleep and rest. This not only will prevent mouth ulcers, but a host of other illnesses as well.

Some people find avoiding soft bristle toothbrushes and mouthwashes that contain sodium lauryl sulfate also helps. Your dentist can give you wax to cover dental or orthodontic mouth devices that have sharp edges.

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See a list of possible causes in order from the most common to the least.


Cold Sores

Cold sores are red, fluid-filled blisters that appear most often near the mouth. They have no cure, are contagious, and may reoccur without warning.

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Mouth Sores

Mouth lesions are sores that can appear on any of the soft tissues of the mouth, including the lips, cheeks, gums, tongue, and floor and roof of the mouth.

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Tongue inflammation

Tongue inflammation

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Canker Sore

A canker sore is a mouth ulcer or sore that is open and painful. The most common sign is a burning or tingling in an area of your mouth that the red sore appears.

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Oral Thrush

Oral thrush occurs when a yeast infection develops inside your mouth. It's marked by white lesions on your tongue, inner cheeks, gums, palate, and/or tonsils.

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Herpes Simplex

The herpes simplex virus (HSV) is an infection that causes herpes, which are blisters that most commonly appear on the genitals or mouth.

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Hand, Foot, and Mouth Disease

Hand, foot, and mouth disease is a contagious condition that usually affects young children. It presents as a rash on the hands and feet along with blisters in the mouth.

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Acute HIV Infection

Acute HIV infection is the primary stage of infection by the human immunodeficiency virus. There are several telltale symptoms, one of which is a rash.

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There are many symptoms of the autoimmune disease HIV/AIDS, including persistent skin rashes, night sweats, and mouth sores.

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Oral Cancers

Oral cancer is a cancer that affects the tissues of the mouth and throat, one symptom of which may be a lump in the neck.

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Esophagitis is inflammation of the esophogas that can be caused by acid reflux or certain medications. You may develop a sore throat or heartburn.

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Gum Disease (Gingivitis)

A severe case of gingivitis is marked by swollen, bleeding gums and swollen lymph nodes around the jaw, and neck.

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Lichen Planus

Lichen planus is a fairly common skin rash that is thought to be triggered by the immune system. It causes lesions in the mouth that may be painful or burn.

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Herpes Stomatitis

Recurrent herpes simplex labialis, also known as oral or orolabial herpes, is an infection of the mouth area caused by the herpes simplex virus. It is a common and contagious infection that spreads easily.

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Measles is a very contagious infection of the respiratory system. One of its several symptoms is a sore or swollen throat.

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Neutropenia occurs when a type of white blood cell called neutrophils that protects your body from infections is low. It can cause symptoms like gum inflammation and mouth sores.

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Syphilis is a sexually transmitted infection. It is caused by a type of bacteria known as Treponema pallidum. According to the Centers for Disease Control and Prevention, in 2006, more than 36,000 cases of syphilis wer...

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Reactive Arthritis (Reiter's Syndrome)

Reiter's syndrome produces inflammation, swelling, and pain in the joints due to infection elsewhere in the body. Symptoms include mouth ulcers, painful urination, and urethral discharge.

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Pemphigoid is a rare autoimmune disorder that most often affects the elderly. Lesions on the abdomen, arms, legs, and mucous membranes is the most common symptom.

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Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease and the most common type of lupus. One of its common symptoms is a rash on the cheeks and nose called a "butterfly rash."

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This feature is for informational purposes only and should not be used to diagnose.
Please consult a healthcare professional if you have health concerns.
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