Diagnosis of canker sores

Canker sores are the commonest cause of mouth ulcers. They are usually benign and resolve on their own in 1 to 3 weeks.

However, these sores are extremely painful and may lead to severe discomfort. There may be difficulty in eating and speaking in severe cases of canker sores.

The sores are commonly diagnosed clinically by examining them. (1-5)

Classification of canker sores

Canker sores on the basis of their appearance and features are classified as (2):

  • Minor Aphthae

They are seen in 80% cases of the canker sores. Patients provide a history of tingling or burning 1 to 2 days before the sores appear.

The sores themselves are 2-8 mm diameter and are shallow, greyish yellow and may occur in clusters of less than five sores. The sores are painful for 3 to 4 days or so. In 10 to 14 days the sores heal without scars.

  • Major Aphthae

These occur in 10% cases of canker sores. The sores appear irregular in shape and have raised borders. They may be 1 to 3 cm in diameter.

These ulcers may be recurrent and often leave scars in their wake after healing. Biopsy is recommended to rule out oral cancer called squamous cell cancer.

  • Herpetiform Aphthae

The name is a misnomer since this is not caused due to Herpes virus. There are large clusters of very small lesions (less than 3mm in diameter).

The clusters may contain 5-100 lesions that fuse to form larger, painful lesions. It takes around 10 to 14 days for these ulcers to heal.

Process of diagnosis

The process of diagnosis of canker sores involves taking a complete medical history, categorizing the level of pain and so forth. (1-5)

Complete medical history

Diagnosis is begun with a complete medical history. This is helpful in diagnosis of:

  • tobacco or alcohol use
  • food and other allergies
  • hormonal fluctuations
  • recent dental work
  • decreased or impaired immunity
  • history of oral sexual intercourse and herpes virus infections and other causes that may lead to increased propensity of canker sores

Categorizing the level of pain of canker sores

Most patients complain of varying severity of the discomfort due to the canker sores. These may be roughly categorized as mild, moderate, or severe.

Mild disease occurs seldom and is not severe or long lasting. Most cases belong to this category.

Presence of four or more canker sores per year is classified as moderate severity canker sores. Those that are more severe are classified as severe disease.

Examining the canker sores

Diagnosis is commonly made by looking at the canker sore. The sore has a typical appearance of a round or oval while cheesy or greyish base or the ulcer and raised red and swollen edges.

The doctor sits opposite the patient with a head lamp or an over head lamp to keep the hands free for examination. Lumps, swollen lymph nodes are noted to exclude other pathologies like cancers.

During the examination dentures are removes and the insides of the cheeks, gums, tongue (above and below the tongue), soft palate (back part of the roof of the mouth) and the throat is examined.

The location, size, color, bleeding, greyish plaque formation over the lesion are all noted. The throat is examined using a tongue depressor and asking the patient to say “aah”.

Palpating canker sores

Once located the doctor wears gloves to physically palpate the lesion or ulcer. This may be painful and is usually performed gently.

If the ulcer is fixed to the underlying muscles and tissue or if there is hardening of the ulcer base, it can be detected by palpation. This is indicative of a deeper and more serious problem like oral cancer.

Tests for other disorders

In patients with recurrent ulcers that tend to persist or recur frequently other disorders are suspected. Tests are conducted for disorders like erythema multiforme, drug allergies, infections with herpes virus, bullous lichen planus etc.

Long term ulcers may also indicate oral cancers. A biopsy may be undertaken in these patients.

This involves snipping off a small bit of tissue from the ulcer and its surrounding areas, staining it with appropriate dyes and examining the same under the microscope. Canker sores are not cancer and do not lead to cancer if they recur.

Further Reading

Last Updated: May 28, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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