Canker Sores: Symptoms and Diagnosis

You might develop a canker sore after eating or drinking something acidic, or biting the inside of your mouth while chewing. Many people get these sores — the medical term is aphthous ulcers — at some point in life. And in most cases, these harmless lesions go away on their own within a week or so, with no complications. (1)

Canker sores often appear initially in adolescence,  but if you develop a mouth sore for the first time, you may wonder whether it’s a canker sore or something more serious. (2)

Here’s how to identify a canker sore and distinguish them from other conditions.

Small, Shallow Bump Inside the Mouth

Canker sores are usually small, typically less than 1 millimeter, although some can grow up to ½ inch to 1 inch in diameter. (3) Larger lesions are more common with major canker sores, which are deeper ulcerations. (1)

The location of a mouth lesion can also indicate a canker sore. These sores don’t typically form outside of the mouth. (1) Instead, canker sores develop on the movable areas of soft tissue in the mouth, such as the inside of the cheek or floor of the mouth, explains Samantha Rawdin, DMD, a prosthodontist based in New York City.

Sensitivity or Tenderness in the Spot

Though canker sores are small, they can cause a lot of discomfort ­­— so much so that you may even feel a canker sore before you see one, notes Jennifer Silver, DDS, a dentist based in Calgary, Alberta.

“Early warning signs include a tingly or burning sensation that may tempt you to chew at the bump,“ she continues. “But if you chew or pick at a budding canker sore, you’ll only make it worse. Even tickling the spot with your tongue can irritate it and make it worse.”

Mild pain is typical with a minor sore, whereas major sores can be extremely painful. (1)

There May Be a Red Border Around the Sore

You can also identify a canker sore by its color. These sores are often yellow or white, and there’s sometimes a red border around the lesion. (2)

Canker Sores Can Also Appear as a Cluster

Some people develop herpetiform canker sores. Instead of developing one sore, they have clusters of tiny lesions — as little as 10 or as many as 100. Sometimes, these tiny lesions grow into one large sore.

This type of sore is uncommon, and despite its name, this canker sore isn’t caused by the herpesvirus. (1)

The good news is that many canker sores heal without scarring in about one to two weeks. The exception is a major sore, which is deeper than other types. These canker sores can take up to six weeks to heal and may leave a scar. (1)

Should You See a Doctor for a Canker Sore?

For the most part, canker sores don’t typically require a doctor’s visit. They’re easy enough to identify and treat on your own.

Some palliative mouth rinses, such as Rincinol or other numbing mouth rinses, can be helpful, and you can even take ibuprofen (Advil) to relieve pain until the sore heals, explains Dr. Rawdin.

In the case of stubborn mouth ulcers that are large, extremely painful, and don’t respond to home treatment, you may need to seek medical care — especially because what you believe to be a canker sore could potentially be a more serious lesion. It’s also important to see a doctor if a fever accompanies a canker sore. (1,3)

How Canker Sores — and Underlying Conditions — Are Diagnosed

There isn’t a specific test to confirm a canker sore. Your dentist or doctor can diagnose the lesion from a visual examination. (4) If your doctor suspects another type of sore, if it doesn’t heal within the standard 7 to 10 days, or if the sore is accompanied by swollen lymph nodes or a fever, you may need a biopsy to rule out oral cancer. (5)

If a visual exam confirms a canker sore, and you’ve had frequent problems with these lesions, your doctor may also suggest testing to find the underlying cause.

The exact cause of a canker sore is unknown and canker sores often occur for no specific reason and without an underlying disease. (2) But these lesions also do occur in people with certain conditions and diseases, including Celiac disease, Crohn’s disease, ulcerative colitis, and HIV or AIDS. People with a nutritional deficiency or food allergies also tend to experience more canker sores. (1)

When canker sores are frustratingly frequent or recurrent or especially painful and bothersome, speak with your doctor or dentist. Your healthcare provider will likely ask you about the severity of your symptoms and if you have a history of canker sores. They’ll also review what medication and supplements you may be taking, and consider whether there are any life events that may be causing you stress, if you’ve made changes in your diet, or had any recent dental work that might be affecting your oral health — all of these can contribute to the development of canker sores. (4)

Your doctor may ask about other symptoms you’re experiencing and test for a specific condition based on your answer. For example, if you have frequent canker sores along with bloating, gas, anemia, and diarrhea, your doctor may test for Celiac disease. If testing reveals you don’t have Celiac disease, you may have gluten sensitivity or inflammatory bowel disease.

Diagnosing and treating an underlying condition may reduce the frequency of outbreaks.