Wellness

What is a canker sore?

canker sore on upper lip

Canker sores. These little mouth ulcers can be a minor nuisance to some and a big pain-in-the-mouth for others.

Dr. Hagen Klieb, a dentist and an oral pathologist at Sunnybrook, answers some questions about canker sores (and about when a mouth sore could be something else.)

What is a canker sore?

Canker sores (also called “recurrent aphthous stomatitis”) are very common and characterized by recurrent open sores (ulcers) in the mouth. Most patients will describe this as a minor nuisance with only irritation to certain acidic foods (eg. orange juice). Other patients, however, will experience a great deal of pain and difficulty swallowing especially if ulcers are frequent, numerous (up to dozens at a time) or large (may be greater than 1 cm).

What do canker sores looks like?

Canker sores typically begin in childhood. Most people who get them typically have a few episodes per year, although this is highly variable. Common areas in the mouth affected are the inner lip, cheeks and undersurface of the tongue. Most will feel a mild burning or stinging sensation before anything is visible. With time, there will be small (3-4 mm), round, yellow-white ulcers that persist for a couple weeks.

What causes them?

Canker sores are the result of an immunologic reaction, but the exact trigger, remains unclear. Some possibilities include allergy, genetic predisposition, stress, trauma, immunologic factors, infectious agents and hormonal influences. It is likely that there are different causes in different people.

I tend to get canker sores once per month (seems linked to my menstrual cycle) – is that a thing?

Canker sores often occur sporadically although some people may notice patterns. Flares are often correlated with stress. There is also likely a hormonal component as a subset of females may notice association with the menstrual cycle and ulcer-free periods during pregnancy have been reported.

Is there something we can do to prevent them?

Systemic disorders that can mimic canker sores (eg. Celiac disease, nutritional deficiencies, Crohn’s disease, etc.) should be excluded by a thorough medical history, and if necessary, laboratory investigations. If no underlying cause is identified, treatment is symptomatic. Most patients do not require treatment, but if symptoms are severe, topical corticosteroids are commonly used to decrease the pain intensity and duration of ulcers. 

When should I worry about a sore in my mouth?

The vast majority of oral ulcers are either canker sores or traumatic (eg. a cheek bite). Oral cancer, however, can present as a chronic, non-healing ulcer or a mass/lump or white/red patch. If you have any lesion in your mouth that persists for more than 2-3 weeks, see your dentist or doctor.

About the author

Alexis Dobranowski

Alexis Dobranowski is a Communications Advisor at Sunnybrook.

Have a question about this post? Get in touch.