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Canker Sores: Causes, Treatment, and Prevention

Canker sores are a common condition characterized by the repeated formation of benign and non-contagious mouth ulcers. The cause is not completely understood but involves an immune response triggered by a variety of factors which may include nutritional deficiencies, local trauma, stress, hormonal changes, allergies, genetic predisposition or other factors.

Canker Sores, also known as aphthous ulcers, are painful, small, shallow, and non-contagious ulcers that develop on the oral mucosa or at the base of gums. They are round or oval with a white or yellow coating and usually surrounded by an inflamed red border. Canker Sores are painful but usually harmless and heal without treatment in one to two weeks.

Causes of Canker Sores

The exact cause of canker sores remains unclear. The painful sores may be attributed to an immune reaction but its development is unclear. Some researchers suggest that the outbreak of canker sores is caused by a combination of factors. These factors may include:

  • Minor mechanical injuries in the oral cavity: the injuries may be caused by poorly fitting denture, braces, sports, or bite injuries.
  • Nutrient deficiencies: vitamin b12, zinc, iron, and folic acid deficiency.
  • Chemical irritation: it may be caused by sodium lauryl sulfate contained in toothpaste or mouthwash.
  • Food allergies: sensitivity to certain foods such as nuts, tomatoes, or citrus fruits.
  • Change in the hormonal balance: it may occur during menstruation.
  • Stress
  • Genetic factors: recurrent aphthous ulcer may occur in people who have a family history of the disorder.
  • Autoimmune reaction: some researchers suggest that canker sores start from a hyperactive immune system which leads to uncontrolled tissue damage.
  • Viruses and bacteria: they could be the cause, but so far not proven.
  • Medical Conditions: canker sores may be associated with some conditions and diseases such as Behcet’s disease, Sweet syndrome, celiac disease, neutropenia, chronic inflammatory bowel disease, and HIV infection.

Symptoms of Canker Sores

Canker sores are painful areas in the oral cavity. They are usually oval or round with a white or yellow center and a red border. Also, they can be found on:

  • The mucous membrane of the oral cavity (inside cheeks and lips).
  • The tongue especially at the tongue border.
  • The soft palate.
  • The gingiva.

The first symptom is a tingling or burning sensation at the affected site. After about 24 hours, the affected site becomes red and a mucosal defect develops with a white or yellow coating. The aphthous ulcer is usually surrounded by an inflamed red border. There are 3 main types of canker sores:

  • Minor canker sores: they are the most common. They are small in diameter (less than 1 cm) and heal without scars in 10 – 14 days. They can be found on the mucous membrane of the lip, chick and the floor of the oral cavity. Also, they can be found on the tongue.
  • Major canker sores: they are deeper and larger than minor type. They can have a diameter up to 3cm. Major canker sores often heal with scarring and require a longer healing time (up to 6 weeks). They are found mainly in the anterior region of the oral cavity, the soft palate, the posterior wall of pharynx and larynx. This causes particularly severe symptoms including pain on swallowing and gagging.
  • Herpetiform canker sores: this type is very rare. Affected people suffer from clusters of 10 – 100 small ulcers (diameter less than 3 mm). The healing occurs normally within 14 days.

Symptoms of Canker Sores
Symptoms of Canker Sores

When to see a doctor?

Visit your dentist if you have:

  • Usually large sores.
  • Sores that last more than 2 weeks.
  • Difficulty eating or drinking.
  • High fever associated with the appearance of canker sores.
  • Pain despite taking painkillers.

Diagnosis of Canker Sores

The dentist recognizes canker sores by its typical appearance. So, the physical examination is often sufficient for the diagnosis. In some cases, more investigation may be needed if canker sores are always recurring or particularly large. The dentist will check whether a specific disease is the cause of these sores.

Treatment of Canker Sores

Canker sores usually heal without treatment in about a week or two. The treatment may be used to relieve the pain and accelerate the healing process.

  • Topical products: there are various over-the-counter and prescription products (pastes, creams, gels, sprays, and rinses) that may contain:
    • Anesthetic agents such as benzocaine or lidocaine.
    • Antibacterial agents such as chlorhexidine.
    • Anti-inflammatory agents such as steroids (dexamethasone).

These agents may help relieve the pain and accelerate the healing process.

  • Mouthwashes: your dentist may prescribe a mouthwash containing:
    • Lidocaine to relieve the pain.
    • Chlorhexidine to kill germs.
    • Steroids (known as dexamethasone) to relieve the pain and reduce the inflammation.
  • Avoid hot and spicy foods: you should avoid foods and drinks that might increase the pain such as spices, acidic food, and alcoholic drinks.
  • Oral Hygiene: you should maintain a good oral hygiene using a soft toothbrush and a foaming-agent-free toothpaste to prevent bacteria from spreading in the oral cavity.
  • Cauterization: this process involves burning sores with a chemical substance to reduce the healing time and relieve the pain.

If canker sores are caused by certain disease, you should visit your doctor to treat the underlying cause. Visit your dentist if you have large sores or they last more than 2 weeks.

Prevention of Canker Sores

Since the cause of canker sores is unknown, and they often recur, you may be able to reduce their frequency by following these instructions:

  • Maintain a good oral hygiene: in order to avoid bacterial inflammation of the oral mucosa, you should pay attention to regular and good oral hygiene. Also, use a soft-bristled toothbrush and avoid toothpaste and mouthwashes that contain sodium lauryl sulfate.
  • Manage stress: relaxation techniques like autogenic training or yoga can help you to manage stress. Also, sports such as running and swimming are an excellent way to free yourself from stress.
  • Eat a balanced diet: eat plenty of fruits and vegetables to prevent nutritional deficiencies.
  • Avoid foods to which you are allergic: if foods such as tomatoes, cheese, or nuts are the possible trigger for canker sores, try to remove them from your diet. Also, spices, salty food, citrus fruits, and alcoholic drinks can irritate your oral mucosa and slow down the healing process of canker sores.
  • Visit your dentist: sharp tooth edges, poorly fitting dentures, and braces can cause injuries to the oral mucosa and lead to the development of canker sores. So, you should visit your dentist if dental prostheses, braces, or any sharp edges are causing injuries and irritation to the oral mucosa.


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