Canker Sore vs Cancer

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  • 0:03 What are Canker Sores…
  • 2:00 Canker Sores vs Cancer
  • 4:01 Lesson Summary
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Lesson Transcript
Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Expert Contributor
Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

Is that cancer or simply a canker sore inside of your mouth? It's important to know, and it's a doctor's job to find out. This lesson explains what these two conditions are and describe some of the basic differences between the two.

What are Canker Sores & Cancer?

Let's say that one day you get up in the morning and head to the washroom. You pick up your toothbrush, open your mouth, and inside you see something that you hadn't noticed before. It's a sore. It's red with a little bit of white. Should you be worried? Is this just a benign (relatively harmless) sore that'll go away on its own, or could it be cancer?

This lesson will offer some basic pointers on how to distinguish between oral cancer and canker sores.

Canker sores, also called aphthous ulcers, are non-contagious lesions that occur inside the mouth. They are commonly small, white to yellow in color surrounded by a reddish border, and painful. Check out this image for example:


Pay attention to the color of this canker sore, its size, and the fact that you can clearly tell where it begins and ends. No one knows what causes canker sores, but various triggers are suspected. These potential triggers include bacteria, stress, trauma to the mouth (such as biting the inside of the lip), vitamin deficiencies, and many more. These triggers may cause inflammation of local sections of the mouth that result in canker sores.

Canker sores are not cancer, and they don't cause cancer. They usually go away within a few weeks after occurring and may come back repeatedly. Cancer is an entirely different process that has less to do with inflammation and more to do with normal healthy cells of your body turning into malicious cells. The malicious cells, or malignant (cancerous) cells, then go on to multiply like crazy, invading deep into the tissues from which they formed and then spreading to other parts of the body.

Oral cancer

Note this image of oral cancer. While it is of the same color as a canker sore, it clearly is far larger and has caused far greater damage to the mouth. It's also hard to tell where it begins and ends, which is poor demarcation.

Canker Sores Vs. Cancer

So, what's that sore inside your mouth? You're about to learn some very general ways to differentiate canker sores from oral cancer. However, there is literally an exception to every rule you're about to learn because medicine is not black and white. In many ways, the process is as much an art as it is a science. Therefore, if you don't know what you are looking at and have no medical background, do not guess. Always visit a doctor as soon as possible to assess any sore in your mouth that you are unsure about. Doctors can take diagnostic samples of the sore if they're not sure themselves as to what it is. Oral cancer can be deadly, and it's extremely important to catch it as early as possible for successful treatment.

Keeping that in mind, here are some general guidelines for distinguishing certain types of oral cancer from your typical canker sore:

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Additional Activities

Distinguishing Between Canker Sores and Cancer

In this lesson, you learned the difference between canker sores and cancer. In this extension activity, you are going to pretend to be a medical professional and try to distinguish between canker sores and cancers from actual patient photos.

Pre-Photo Analysis

  • Use the information in the lesson to write some guidelines that will help you distinguish between a canker sore and cancerous legions or tumors. Questions to guide you in this task include:
    • What are the similarities between all canker sores
    • What does a cancerous lesion look like?
    • What does a tumor look like?

What to Do with the Photos

  1. For each photo shown in this extension activity, identify the part of the image that is either the canker sore or a cancerous lesion or tumor.
  2. Use the guidelines you developed in the pre-photo analysis to explain how you determined whether the image featured a canker sore or a cancerous lesion or tumor.

Photos to Analyze

Here are a series of real photos of conditions in or around the mouth. We'll label these numerically.

Picture 1

Picture 2

Picture 3

Picture 4

Picture 5

Picture 6

Post-analysis Questions and Task

  1. What would be a clue beyond looking at a sore in the mouth or lip area that the sore or lesion in someone's mouth or lip area is a canker sore versus a cancerous lesion or tumor?
  2. Research ways to prevent canker sores and mouth cancers.

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