Canker sores, also known as aphthous ulcers, are common, painful lesions that develop inside the mouth. These shallow ulcers are typically round or oval, featuring a white or yellowish center surrounded by a distinct red border. They are not contagious and do not result from a virus like herpes, but they can make eating and talking very difficult. Most minor canker sores heal within one to two weeks, though major sores can be larger, deeper, and last for a month or more.
Where Canker Sores Develop
Aphthous ulcers prefer the soft, movable tissues within the mouth, which are lined by non-keratinized mucosa. This tissue is less durable and more susceptible to minor injury or irritation, making it the primary site for canker sore formation. Common locations include the inside of the cheeks and lips, the underside of the tongue, and the soft palate. Constant movement and rubbing against teeth or dental appliances increase the likelihood of injury that can trigger an ulcer.
The tonsils, located at the back of the throat, are generally considered an uncommon site for a true aphthous ulcer. In the rare instances a canker sore does form on the tonsil, it typically presents as a single, painful ulceration with the characteristic white-yellow base and red rim. Minor canker sores are usually small, less than one centimeter in diameter, and are the most frequent type, accounting for about 85% of all cases.
Major canker sores are larger, sometimes exceeding one centimeter, and may have an irregular border, causing more intense and prolonged pain. Herpetiform ulcers, which present as clusters of tiny sores that merge into a larger ulcer, are also rare but can appear in the throat area. Any lesion in the tonsil area that looks like a canker sore, especially if it causes severe pain when swallowing, often leads to confusion with other throat conditions.
Why Sores Appear on Tonsils
If a painful sore or white spot appears on the tonsils, it is more likely caused by a condition other than a classic aphthous ulcer. The tonsil area is part of the body’s immune defense system, making it a frequent site for infectious processes. Viral causes are the most common reason for a sore throat and often produce lesions or white patches on the tonsils.
One common viral cause is Herpangina (Coxsackievirus), which creates small, painful, blister-like sores at the back of the mouth and throat, including the tonsils and soft palate. Infectious mononucleosis (Epstein-Barr virus) can lead to severely swollen tonsils with a white or yellowish coating, resembling pus or large ulcers. The Herpes Simplex Virus (HSV) can also cause painful ulcers in the throat, especially during the initial infection.
Bacterial infections are a frequent culprit for white patches or sores on the tonsils, most notably Group A Streptococcus, which causes strep throat. Strep throat often presents with red, swollen tonsils that may have white patches, streaks of pus, or small red spots on the roof of the mouth. These exudates can be mistaken for ulcers, but they signal a bacterial infection requiring antibiotic treatment. Another concern is a peritonsillar abscess, a collection of pus behind the tonsil, typically causing severe, unilateral throat pain and difficulty opening the mouth.
Other less common causes for sores or white spots in the tonsil area include oral thrush (a fungal infection causing creamy white lesions) and, in rare cases, precancerous lesions or oral cancer. Persistent or recurring ulcers may also be associated with systemic diseases like inflammatory bowel disease or Behcet’s disease. Since the visual characteristics of many conditions overlap, accurately identifying the underlying cause is important.
When to See a Doctor
While most minor mouth sores, including true canker sores, heal without medical intervention, certain symptoms warrant professional medical evaluation. Seek immediate care if you experience difficulty breathing (suggesting airway obstruction) or extreme difficulty swallowing that prevents drinking fluids. Excessive drooling, especially in a child, is another sign that swallowing is severely impaired.
Consult a healthcare provider if the sore lasts longer than two weeks without showing signs of healing. A high fever (101 degrees Fahrenheit or higher) that persists for several days alongside the sore throat suggests a significant infection. Other concerning symptoms include severe, one-sided throat pain (indicating a peritonsillar abscess), a rash, joint pain, or blood in your saliva or phlegm.