Canker sore vs. oral cancer: How can you tell the difference?

Most people experience a canker sore at some point in their lives. These small, often painful lesions can appear on any moist, fleshy surface inside the mouth. This includes the cheek, tongue, roof or gums.

Normally, canker sores heal on their own in about two to three weeks. So, how do you know if a mouth ulcer is a symptom of oral cancer or a harmless canker sore? 

We checked in with Ann Gillenwater, M.D., director of MD Anderson’s Oral Cancer Prevention Clinic. 

How do canker sores differ from oral cancers?

First of all, “canker sores” is not a medical term. It’s a term that some people use to describe many different unrelated conditions. We can continue to call them that here, for the sake of this article, but it’s important to note that the scientific name for what we’re discussing is actually “aphthous ulcers.” 

Aphthous ulcers are painful little sores that develop inside the mouth. We don’t know exactly what causes them, but most resolve on their own pretty quickly.

Do canker sores develop in other locations on the body, too?

No. Aphthous ulcers only develop on the moist surfaces inside the oral cavity. 

The painful cracks that sometimes develop in the corners of your mouth are called angular cheilitis or perlèche, and they tend to be caused by an overgrowth of yeast called “candida” or a vitamin B deficiency. 

Ulcers that develop on the lips or as clusters of blisters around the mouth are usually caused by the herpes virus, especially if they’re preceded by a tingling sensation. These are also known as fever blisters or cold sores.

Are there any other conditions that can cause ulcers inside the mouth?

Oh, yes. Many things that aren’t cancer can cause ulcers inside the mouth. These include chickenpox, shingles, an inflammatory condition called lichen planus, and hand, foot and mouth disease, to name just a few.

How can someone tell if a mouth ulcer is an oral cancer instead of just a canker sore?

Here are the qualities I look for:

Appearance

The edges of a canker sore are often red and angry looking because the surrounding tissue is inflamed. That's not usually the case with cancers. Canker sores also tend to be flat. Oral cancers often have a tiny lump or bump under the lesions that you can feel.

Behavior

Oral cancer in its earliest stages is not usually painful. But canker sores often are. They become less painful as they heal.

Changes

See a doctor if you have a small spot that grows larger, a white spot that turns red, or a lesion that bleeds when it didn't use to.

Development

Does the lesion get worse or better over time? Most canker sores will heal on their own within two or three weeks. If yours doesn't, it's time to see a doctor.

Is there anything that cancer patients should know about canker sores?

Cancer patients who are receiving chemotherapy often develop mouth ulcers. I do a fair number of consultations each month with patients who are worried that these might be cancer. 

The good news is that this type of mouth sore is just the body’s reaction to chemotherapy. So, it’s nothing to be worried about; it’s a well-known side effect of that particular treatment.

Request an appointment at MD Anderson online or by calling 1-877-632-6789.