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Is It a Canker Sore or Cancer? Look for These Signs

Non-cancerous ulcers usually heal within a few days or weeks — if it’s sticking around, it’s time to get it checked

Person pulling bottom lip down to show mouth ulcer

Most of the time, that obnoxious little sore in your mouth is a canker sore. Unlike cold sores, canker sores aren’t contagious — just uncomfortable. And they’re extremely common: Approximately 20% of the U.S. population has had at least one canker sore in their lifetime. Anyone can get them, and while they can sometimes be a sign of an underlying medical condition, they’re usually nothing to worry about. They resolve on their own and you move on with your life.


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But not all mouth ulcers are canker sores. Sometimes, these conditions require medical intervention. Even oral cancers can seem pretty similar to the common canker sore. At least, they seem similar if you don’t know what you’re looking (and feeling) for.

Enter ear, nose and throat specialist (otolaryngologist) Ashley Mays, MD. With her help, we walk through the differences between canker sores, oral cancers and other mouth ulcers.

How to identify a canker sore

So, how can you tell if you have a canker sore? Let’s start with what you’ll see when you look in a mirror. According to Dr. Mays, the key characteristics to pay attention to are:

  • Location. Canker sores can appear on your gums, tongue, inner cheeks, inner lips or the roof of your mouth. You can’t get a canker sore on your outer lips (skin).
  • Size. The average size of a canker sore is small — less than one millimeter in diameter. The National Institutes of Health (NIH) considers a canker sore severe when its diameter is between 1 and 3 centimeters.
  • Shape. If you’ve got a canker sore, your mouth ulcer will be round or oval-shaped.
  • Depth. Canker sores are flat and slightly sunken.
  • Color. The sore itself will be yellow or white. It may turn gray as it heals. The perimeter of the ulcer will be red and inflamed and may be slightly raised from the swelling.
  • Texture. A canker sore isn’t patchy or textured. And it won’t bleed or discharge any kind of fluid.
  • Number. It’s possible to have multiple canker sores at the same time. In some cases, you may get a cluster of tiny ulcers (that may or may not go on to merge into a single sore). These are called herpetiform canker sores. While they sound more serious, they’re no more worrisome than a run-of-the-mill minor canker sore.

Of course, a canker sore is more than just something you see. You feel them, too! Dr. Mays explains that the symptoms they cause are pretty consistent.


“While there are exceptions, canker sores typically hurt,” she says. The pain tends to be of the burning and tingling variety. And if you’ve ever tried to down a glass of orange juice while you’ve got one, you know all too well that they’re extra ouchy when they’re irritated.

“It’s best to avoid spicy or acidic food and drink when you have a canker sore,” Dr. Mays advises. “You may find that hard or sharp foods — like potato chips or crusty bread — also bother you.”

Depending on where the ulcer is in your mouth, you may find eating, drinking, brushing your teeth or talking uncomfortable. Uncomfortable, but not undoable. A canker sore can be seriously annoying, but it shouldn’t be debilitating.

What makes a mouth sore abnormal?

Now that you have a good idea of what a canker sore looks and feels like, let’s talk about mouth ulcers or lesions that are more suspicious.

There are lots of different kinds of mouth ulcers and they aren’t always cause for concern. (That’s right: Not all roads lead to oral cancer!) But you still need to see a doctor or dentist. They’ll determine what exactly is going on and prescribe a course of treatment.

What abnormal mouth sores look like

Here are some of the physical characteristics to be on the lookout for:

  • Red, white, or mottled patches in your mouth.
  • A bump under the skin where the ulcer is.
  • An area in your mouth that becomes discolored and stays that way.
  • Bleeding from the sore that won’t heal and lasts for more than two weeks.
  • Any kind of texture change. (Think rough patches, cracking, crustiness, or a cottony sensation.)
  • Visible lumps or swelling in your neck, cheek or jaw.
  • Changes to one or more of your teeth. (Maybe a tooth is suddenly loose. Maybe your dentures, braces, clear aligners or retainers suddenly don’t fit.)

That’s what you might be seeing. But some oral cancers and abnormal ulcers aren’t that obvious to us. That’s in part because they can hide behind your teeth or under your tongue. And keep in mind that — unlike canker sores — other kinds of mouth ulcers and oral cancer can appear on your outer lips.

What abnormal mouth sores feel like

Dr. Mays recommends paying close attention to other symptoms, like:

  • Nagging mouth pain. (Unlike canker sores, oral cancer typically doesn’t hurt from the get-go. The pain emerges over time — and then, it doesn’t go away.)
  • Swelling in your neck that lasts for more than two weeks.
  • A lump or thickening in your cheek that doesn’t go away.
  • Numbness in your tongue or another part of your mouth.
  • Constantly feeling like something’s caught in your throat (globus sensation).
  • A change in your voice — like hoarseness, for example — that lasts longer than two weeks.
  • Chronic bad breath (halitosis) despite having good oral hygiene habits.
  • An earache or sore throat.
  • Unintentional and unexplained weight loss.
  • Your mouth ulcer changing, but not healing.
  • Difficulty chewing, talking, or moving your jaw or tongue. (Canker sores may make these activities unpleasant, but they don’t impact function. That’s what we’re talking about here.)


Some of these symptoms really hit you over the head. But others can easily slip under the radar — especially if they aren’t preventing us from living our busy lives.

“We see patients all the time who had an irritation around their tooth that ends up being squamous cell cancer, which may have been bothering them for up to a year,” Dr. Mays shares.

“That’s why it’s important to notice when your symptoms don’t resolve. If they last for more than two weeks, get them checked out by a doctor or dentist.”

When to see a doctor (or dentist)

Your dentist performs an oral cancer screening every time you go in for a cleaning, which should be twice a year.

According to Dr. Mays, the oral cancer screening process takes less than 10 minutes. Your doctor or dentist will perform a visual assessment and feel your tongue looking for abnormal color and firm lesions. You also fill out an information form so the provider can pay close attention to any specific areas of concern. If you’re keeping those appointments — and feel comfortable that your mouth ulcer is a canker sore — there’s little reason to follow up.

If your symptoms aren’t resolving, or are getting worse, that’s another story. Then, it’s time to call a provider.

Ideally, you want to get an appointment with an ear, nose and throat (ENT) specialist like Dr. Mays. If you don’t already work with an ENT, make an appointment with your primary care provider. They can refer you if their attempts to diagnose or treat your mouth sore aren’t effective.


Here are a few other reasons to consider making an appointment with a provider:

  • You’re experiencing more, larger or more severe canker sores than usual. Many different medical conditions can trigger canker sores. The same is true of medications. Not having oral cancer is a relief, to be sure. But it’s still important to know why your mouth’s status quo is changing.
  • You’re in a lot of pain. Like stubbing your pinky toe, canker sores can be far more painful than they have any right to be. If over-the-counter treatments and home remedies aren’t putting a dent in your discomfort, it’s important to let your provider know. They may prescribe a medication to help manage your symptoms.
  • The mouth ulcer isn’t your only symptom. Are you running a fever? Are your lymph nodes swollen? Are you usually tired? Are you having tummy troubles? Remember, canker sores and oral cancer aren’t the only kinds of sores you can develop in your mouth. And sometimes, mouth sores are a symptom of a larger medical condition. It’s best to get checked out to make sure you aren’t missing anything.

Taking the time to be extra cautious can really pay off — especially if that sore in your mouth is cancerous.

“Nobody wants a cancer diagnosis. But the good news is that, when picked up early, oral cancers are highly curable,” encourages Dr. Mays. “Early detection is key. So, if you have symptoms, don’t ignore them.”


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