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Mouth Ulcers: Causes, Treatment, and Prevention

Mouth ulcers are very common, occurring in association with many diseases and by many different mechanisms, but usually, there is no serious underlying cause. Mouth ulcers often cause pain and discomfort and may alter the person's choice of food while healing occurs (e.g. avoiding acidic or spicy foods and beverages).

Mouth ulcers are oval or round lesions, which form on the mucous membrane of the oral cavity, including the lip, cheek, tongue, palate, and floor of the mouth. Mouth ulcers are characterized by a loss of the mucosal layer. In most cases, they are painful and last from one to two weeks. However, in some cases, they may be an indication of oral cancer or infection such as herpes simplex virus (HSV).

Causes of Mouth Ulcers

Many factors can cause mouth ulcers, from minor mechanical injuries to serious medical conditions.

Traumatic Ulcers

Traumatic ulcers are common in the oral cavity. They are painful and surrounded by an inflamed red border. They occur due to mechanical, thermal, or chemical injuries. The most frequent cause is mechanical injuries from:

  • Sharp or broken teeth.
  • Ill-fitting dentures.
  • Braces.
  • Tongue or cheek biting.
  • Eating sharp foods.

Thermal injuries are common from over-hot foods or drinks. Chemical causes of traumatic ulcers include:

  • Direct contact of aspirin with oral mucosa.
  • Irritation by a strong mouthwash (hydrogen peroxide at concentration 1-3%).
  • Holding a medication in the mouth instead of swallowing it (occurs mostly in children).

You should visit your dentist to eliminate the cause if possible. Also, if mouth ulcers don’t heal within 3 weeks, you should visit your doctor for more tests and investigations.

Drug-related Ulcers

Some drugs cause mouth ulcers as a side effect, for example:

  • Nicorandil: it is a vasodilator drug used to treat angina.
  • Indometacin: it is a non-steroidal anti-inflammatory drug (NSAIDs) that used to reduce fever, pain, and swelling from inflammation.
  • Phenytoin: it is an anti-seizure medication.
  • Cytotoxic drugs: they are used to treat cancer.

Also, placing an aspirin next to a painful tooth to relieve the pain can lead to mouth ulcers. These drugs tend to produce solitary or multiple mouth ulcers. So, if you develop mouth ulcers as a side-effect of some medications, you should visit your doctor to change the prescription.

Aphthous Ulcers

Aphthous ulcers, also known as canker sores, are painful, shallow, non-contagious mouth ulcers. They are round or oval, covered with a white or yellow coating, and surrounded by an inflamed red border. There are 3 types of aphthous ulcers (canker sores):

  • Minor aphthous ulcers: this is the most common type. The diameter of ulcers is less than 10 mm. They heal without scarring in 10-14 days.
  • Major aphthous ulcers: this type is less common than minor aphthous ulcers. The diameter of ulcers is larger than 10 mm. They require a longer healing time (up to 6 weeks) and may leave scars.
  • Herpetiform aphthous ulcers: this type is very rare. Herpetiform aphthous ulcers appear in clusters of 10-100 ulcers (diameter less than 3 mm). They heal within 14 days.

The exact cause of aphthous ulcers is unknown but researchers suggest that the outbreak of these ulcers is caused by a combination of factors, including:

  • Mechanical injuries in the oral cavity.
  • Stress.
  • Hormonal changes during menstruation.
  • Food allergies such as sensitivity to nuts.
  • Nutritional deficiencies such as vitamin B12, iron, and folic acid deficiency.
  • Irritation by chemical substances such as sodium lauryl sulfate contained in toothpaste and mouthwashes.
  • Medical conditions such as Behcet’s disease.

The treatment aims to relieve the pain and reduce the healing time. The treatment may include topical products (creams, pastes, gels, sprays, and rinses) that contain an anesthetic, antibacterial, and anti-inflammatory agents.


Mouth ulcers may be caused by some infections such as:

  • Viral infection: herpes simplex virus (HSV), chickenpox, and human immunodeficiency virus (HIV).
  • Bacterial infection: acute necrotizing ulcerative gingivitis (ANUG), syphilis, and tuberculosis.
  • Fungal infection: blastomycosis and cryptococcosis.

Infectious causes of mouth ulcers
Infectious causes of mouth ulcers. Source: Wikipedia


In rare cases, a painless, slow-growing and non-healing mouth ulcer may be a malignant lesion. Malignancies in the oral cavity are usually carcinoma. Squamous cell carcinoma is the most common type of oral cancer. The cause of oral cancer is not clear but doctors suggest that many factors may increase the risk of oral cancer, include:

  • Smoking or chewing tobacco.
  • Heavy alcohol drinking.
  • The excessive sun exposure.
  • Immunodeficiency (the immune system’s ability to fight infectious disease and cancer is compromised or entirely absent).

Chemotherapy and Radiation

Chemotherapy and radiation can cause burn-like, painful mouth ulcers, making it difficult to eat, drink, swallow, and talk. These ulcers may appear on:

  • Lips
  • Gums
  • The tongue
  • The palate
  • The floor of the mouth

Cancer treatment kills both cancer cells and some healthy cells that line the inside of the oral cavity. So, it becomes difficult for oral cavity to heal and fight germs, leading to infections and ulcers. Also, chemotherapy and radiation can impair the immune system that protects the human body against bacterial, viral, and fungal infections, leading to mouth ulcers or making mouth ulcers worse.

Medical Conditions

Mouth ulcers may be associated with some diseases and conditions, include:

  • Autoimmune diseases: Behcet’s disease and Kawasaki disease.
  • Gastrointestinal diseases: celiac disease, crohn’s disease, and ulcerative colitis.
  • Dermatological diseases: chronic ulcerative stomatitis, erythema multiforme, and lichen planus.
  • Hematological diseases: anemia, hematinic deficiencies, and neutropenia.
  • Systemic infections:
    • Viral infections: herpes simplex virus (HSV) and human immunodeficiency virus (HIV).
    • Bacterial infection: syphilis, and tuberculosis.
    • Fungal infection: blastomycosis and cryptococcosis.

Symptoms of Mouth Ulcers

The symptoms of mouth ulcers depend on the cause. In most cases, they are painful lesions that make eating, drinking, swallowing, and talking more difficult (depending on size, location, and severity of ulcers). However, ulcers caused by oral cancer are painless (in the early stage).

When to See a Doctor?

Visit your doctor if you have:

  • Large ulcers.
  • Ulcers that last more than 2 weeks.
  • Difficulty eating, drinking, swallowing or talking.
  • Pain despite taking painkillers.

Diagnosis of Mouth Ulcers

The dentist will examine the oral cavity, searching for white or red spots on lips, gums, the tongue, the palate, and the floor of the mouth. He/She will check the size, color, number, and location of ulcers. Also, He/She will search for broken teeth or restorations with sharp edges that may cause mouth ulcers. The dentist will ask you some questions about:

  • The duration that ulcers have been present.
  • If there have been previous ulcers which have healed.
  • Problems in other parts of the body such as:
    • Genital ulcers.
    • Eye lesions.
    • Digestive problems.
  • If you have a systemic disease.
  • Medications that you take.

If mouth ulcers don’t heal within 2 weeks or the dentist suspects you are suffering from oral cancer. He/She will perform some tests and investigations such as:

  • Blood tests
  • Biopsy

Treatment of Mouth Ulcers

The treatment can range from painkillers and anti-inflammatory drugs to changing a medication, smoothing sharp tooth edges (if the cause is trauma), or treating the causative disease.

  • Maintain a good oral hygiene: use a soft-bristled toothbrush, foaming-agent-free toothpaste, and antiseptic mouthwash (chlorhexidine) to prevent secondary infection and reduce the healing time.
  • Topical products: use over-the-counter products (gels, creams, pastes, sprays, and rinses) that contain:
    • Analgesic agents such as lidocaine or benzocaine.
    • Antiseptic agents such as chlorhexidine.
    • Anti-inflammatory agents such as steroids (dexamethasone).

To relieve the pain and accelerate the healing process.

  • Avoid hot or spicy foods: you should avoid foods and drinks that might increase the pain such as:
    • Spicy foods.
    • Acidic foods as citrus fruits
    • Alcoholic drinks.
  • Smooth sharp tooth edges: you should visit your dentist to:
    • Smooth sharp or broken teeth edges.
    • Replace broken restorations.
    • Repair or replace ill-fitting dentures.
    • Place wax on braces.
  • Substitute a medication: if you develop mouth ulcers as a side-effect of some medications, you should visit your doctor to change the prescription.
  • Treat viral, bacterial, or fungal infections: if mouth ulcers are caused by viral, bacterial, or fungal infections, visit your physician to treat these infections. Also, visit your dentist for professional cleaning if the underlying cause is acute necrotizing ulcerative gingivitis.
  • Cancer treatment: in the case of oral carcinoma, you may need to undergo chemotherapy or radiation.

Prevention of Mouth Ulcers

To prevent mouth ulcers you should:

  • Maintain a good oral hygiene: Brush your teeth regularly with a soft-bristled toothbrush. Also, avoid toothpaste and mouthwashes that contain sodium lauryl sulfate.
  • Eat a well-balanced diet: eat a plenty of fruits and vegetables to prevent nutritional deficiencies. If you think your diet is lacking vitamin B12, folic acid, or iron, you should consider taking a supplement. But it is always better to take these from the diet.
  • Avoid foods to which you are allergic: if you have a sensitivity to some foods such as tomatoes, nuts, or cheese, try to remove it from your diet.
  • Avoid anything that may irritate the oral mucosa: try to avoid or limit:
    • Hot, salty, and spicy food.
    • Acidic foods as citrus fruits.
    • Alcoholic drinks.
    • Sharp food such as crispy bread.
    • Strong mouthwashes.
    • Hard toothbrushes.
  • Manage stress: relaxation techniques and sports can help you to manage stress.
  • Avoid smoking and alcohol consumption: chewing or smoking tobacco and alcohol drinking may increase the risk of oral cancer.
  • Avoid excessive sun exposure to your lips: use a sunscreen to protect your lip.
  • Visit your dentist regularly: visit your dentist once every 6 months for a professional cleaning to prevent infections in the oral cavity such as acute necrotizing ulcerative gingivitis. Also, visit your dentist to:
    • Smooth sharp or broken teeth edges.
    • Replace broken restorations.
    • Repair or replace ill-fitting dentures.
    • Place wax on braces.


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