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Updated on September 30, 2022

Mouth Ulcers: Causes, Symptoms & Treatment

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What are Mouth Ulcers?

Mouth ulcers, also known as canker sores or aphthous ulcers, are small but painful lesions inside the mouth. 

These lesions may make eating, drinking, and talking uncomfortable. They are not contagious and usually heal within a few days to a week. 

Mouth ulcers may develop after an accidental injury to the soft tissue lining in the mouth. However, other mouth ulcers may appear naturally. 

In addition, people with a known family history of canker sores are more susceptible to developing mouth ulcers.

Mouth ulcers are self-healing. If the sore increases in size and becomes more painful, you may need immediate medical attention. If an ulcer does not go away on its own, it might be a sign of mouth cancer.1

What Do Mouth Ulcers Look Like?

Mouth ulcers are mostly round or oval and can affect the mouth, lips, or cheeks.2 They can be white, yellow, grey, or red and may appear swollen. 

A mouth ulcer may start as a single ulcer and stay in the same state until it goes away. However, they can multiply in the mouth, but most mouth ulcers are harmless. 

Mouth ulcers can sometimes be confused with cold sores. Cold sores are small blisters that appear on the lips or around the mouth. They start with a tingling and burning sensation. 

However, canker sores may not be painful until they are triggered by certain foods such as citrus or acidic fruits and vegetables. 

Mouth ulcers are typically under 5mm wide, and some may join together to form one large one. 

Some types of mouth ulcers appear on the soft tissues of the mouth, such as:

  • The sides of the tongue
  • On the walls of the cheeks
  • The area around the tonsils
  • Under the tongue

Medical Images of Mouth Ulcers

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What Causes Mouth Ulcers?

The exact cause of mouth ulcer sores is unknown, and it can differ from person to person. However, a single mouth ulcer can result from minor injuries to the mouth’s soft tissues. 

Some causes of mouth injuries include:

  • Chewing hard food
  • Poorly fitted dentures
  • Accidentally biting or hurting the inner side of the cheek
  • Brushing teeth roughly
  • Frequent rubbing against a sharp or broken tooth
  • Hot food burns

Some mouth ulcers are triggered by something else, and are typically recurring.

These are some triggers that might cause mouth ulcers to keep coming back:

  • Hormonal changes (like menstruation and pregnancy)
  • Eating certain types of foods, especially spices, citrus fruits, tomatoes, and others
  • Using toothpaste or mouthwash containing sodium lauryl sulfate.3
  • Fungal, bacterial, or viral infections
  • Lack of vitamins like B-12, iron, zinc, and folate
  • A negative response to a specific type of medication
  • Mouth cancer

Mouth ulcers can also be a sign of other medical conditions, including:

  • Diabetes mellitus
  • Celiac disease (gluten intolerance)
  • Behcet's disease (a condition where the whole body suffers inflammation)
  • Inflammatory bowel disease
  • Weakened immune system
  • Pediatric gingivostomatitis 

Accompanying Symptoms of Mouth Ulcers

Symptoms of mouth ulcers vary. However, the primary sign that indicates a mouth ulcer is a red or white sore in the mouth. The sore might become painful, especially when eating or drinking.

Canker sores may also lead to swelling of the skin around them, especially when they are on the lining of the cheeks. 

In addition, since most foods and drinks can make mouth sores painful, loss of appetite is common.

Because mouth ulcers usually disappear within a short time, you might not experience the symptoms discussed above. However, the symptoms may worsen during times of stress, sickness, or severe exhaustion.

Sometimes, mouth ulcers will be accompanied by mild fever symptoms. If this happens, further medical assistance is necessary.

When Should You Be Concerned About a Mouth Ulcer? 

See a doctor or dentist if you experience any of the following:

  • If the canker sores last for more than three weeks. Mouth ulcers typically last one to two weeks. However, if they exceed this period, you should see a doctor.
  • Unusual sores. If you are used to getting canker sores repeatedly, you know what typical sores look like. If you notice a different type developing in your mouth, take extra caution.
  • Consider medical assistance if your mouth ulcers are spreading rapidly and in larger numbers.
  • They are bigger and more painful. If the types of mouth ulcers that are currently developing are bigger and more painful, they could be something more serious.
  • A fever accompanies them. Mouth ulcers are not usually accompanied by a fever, so if they are, consider medical attention.
  • If the mouth ulcer is accompanied by bad breath. The bad breath may be caused by food debris that remains in your mouth for a long time. If you leave this untreated for longer, an infection can develop.

How are Mouth Ulcers Diagnosed?

A mouth ulcer is diagnosed through a simple visual exam. However, further tests may be needed if you have other worrisome symptoms.

If your oral health expert is unable to identify the origin of your mouth ulcers, or if the ulcers do not respond to standard treatments, you may need a biopsy of the ulcer and some surrounding tissue. 

A biopsy is a process that involves the removal of a tissue sample for examination and diagnosis.

How to Get Rid of Mouth Ulcers (Best Treatment Options)

The cause of the mouth ulcer will significantly determine the type of treatment you need. 

In some cases, it might be as easy as smoothening a sharp tooth. In other cases, your dentist may recommend advanced treatment.

Mouth ulcer treatments include:

  • Ointments such as Debacterol or Abreva are designed to cauterize the sores and help them heal fast.6 Cauterizing is the “burning” of the affected skin cells to prevent infection. 
  • A person with bacterial canker sores will be prescribed antibiotics such as Vibramycin (doxycycline) or Oracea (doxycycline).
  • If a virus is the cause of the canker sores, your dentist will prescribe antiviral medications such as Valtrex (valacyclovir).
  • Antimicrobial mouthwash such as Listerine can help reduce the number of potentially infectious germs in the mouth. If you’re experiencing pain on the canker sores, silver nitrate may help.
  • If you are deficient in certain nutrients such as folate (folic acid), vitamin B-6, vitamin B-12, or zinc, your doctor may advise you to take nutritional supplements.

Does Mouth Ulcer Medication Have Side Effects?

Just like any other medication, mouth ulcer medications have side effects.  

Common side effects may include:

  • Dry mouth
  • Upset stomach
  • Diarrhea
  • Nausea
  • Dizziness
  • Vomiting
  • Skin rashes

Although it is uncommon, canker sore medications can also induce life-threatening allergic reactions. 

Trouble breathing, hives, and swelling of the face or neck are all symptoms of allergic responses associated with these medications. 

If you think you have an allergic reaction to your canker sore medication, you should immediately seek medical attention.

This is not an exhaustive list of side effects. The best way to learn more about the potential side effects of canker sore medications is to speak with your oral healthcare professional.

Here are some home remedies to help heal canker sores fast:4

  • Rinse your mouth with a mixture of salt, baking soda, and water
  • Apply milk of magnesia on the sore5
  • Place ice on the sores
  • Apply some damp tea bags on the sores
  • Use natural remedies such as myrrh, chamomile tea, or echinacea

Tips for Preventing Mouth Ulcers

Some mouth ulcers do not have a cure, and they tend to recur throughout a person’s life. 

Luckily, there are a few things you can do to prevent mouth ulcers or reduce their recurrence.7 For example, consider improving your mouth hygiene as poor oral hygiene is a known cause of mouth infections.

Some types of prescription medications, such as antidepressants, can also cause mouth ulcers.8 If your prescribed medication is causing sores in your mouth, consult your doctor for other options.

Change your toothbrush or toothpaste if you notice that they are the triggers to your mouth ulcers. 

For instance, if you are using a toothpaste containing sodium lauryl sulfate (SLS), you should change it to a better toothpaste. There is a denaturing effect of SLS on oral epithelium that is responsible for mouth ulcers. 

Products that contain sodium fluoride and are approved by the American Dental Association (ADA) are the best options.9 

Your toothbrush could also be too harsh on your mouth lining. Try using a soft bristle toothbrush to see if the sores subside.

9 Sources Cited
Last updated on September 30, 2022
All NewMouth content is medically reviewed and fact-checked by a licensed dentist or orthodontist to ensure the information is factual, current, and relevant.

We have strict sourcing guidelines and only cite from current scientific research, such as scholarly articles, dentistry textbooks, government agencies, and medical journals. This also includes information provided by the American Dental Association (ADA), the American Association of Orthodontics (AAO), and the American Academy of Pediatrics (AAP).
  1. Signs and Symptoms of Oral Cavity and Oropharyngeal Cancer,” American Cancer Society
  2. Management of Aphthous Ulcers,”American Academy of Family Physicians, 1 July 2000
  3. Effects of oral rinsing with triclosan and sodium lauryl sulfate on dental plaque formation: a pilot study,” National Institute of Health (NIH)
  4. Mouth ulcers,” Department of Health, State Government of Victoria, Australia
  5. Canker sore,” Mayo Foundation for Medical Education and Research (MFMER)
  6. The Treatment of Chronic Recurrent Oral Aphthous Ulcers,” National Institute of Health (NIH), 3 October 2014
  7. Mouth ulcers,” Oral Health Foundation
  8. Ulceration of the oral mucosa induced by antidepressant medication: A case report,” National Center for Biotechnology Information (NCBI), 03 November 2009
  9. Should toothpastes foam? Sodium lauryl sulfate: A toothpaste detergent in focus,” National Institute of Health (NIH)
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