Canker Sores vs. Cold Sores: Know the Difference

If you’ve ever had a painful sore in or around your mouth, you might have wondered: Is it a canker sore or a cold sore? While both can be uncomfortable — and sometimes even look alike at first glance — they’re two very different conditions.

Knowing what you’re dealing with can help ensure you’re treating them properly, so you can feel better and keep the people around you safe.

Medical dermatologist Anthony Fernandez, MD, PhD, explains what canker sores and cold sores are and what to do about them.

What are the differences between canker sores and cold sores?

Canker sores happen inside your mouth and aren’t contagious. Cold sores usually appear outside your mouth and are contagious.

Let’s take a quick look at the differences between canker sores and cold sores:

Symptoms of canker sores vs. cold sores

Both canker sores and cold sores can be uncomfortable, even painful. But they look and feel different.

Canker sores are small, shallow ulcers that form inside your mouth. You might find them on your:

• Inner cheeks
• Gums
• Soft palate (the back part of the roof of your mouth)
• Tongue

If you have a canker sore, it’ll usually start with a tingling or burning sensation in your mouth. It soon develops into a painful sore that’s round or oval-shaped, with a white, yellow or gray center and a red border. You’ll typically only have one canker sore at a time, but sometimes, they show up in small groups.

And they can be quite painful.

“Canker sores can make eating, drinking or even talking uncomfortable,” Dr. Fernandez acknowledges.

Cold sores — sometimes called fever blisters — typically form outside the mouth. But if you’re living with immunocompromise or you’ve only recently been infected with the cold sore virus, you may get them inside your mouth.

You usually find cold sores:

• On or around your lips
• Under your nose
• On your chin

“Cold sores tend to show up in the same place with each outbreak,” Dr. Fernandez clarifies.

They typically begin with a tingling or burning feeling, then develop into small, fluid-filled blisters. Those blisters may break open, ooze and get crusty.

Cold sores may also come with flu-like symptoms, like:

• Low-grade fever
• Sore throat
• Swollen lymph nodes

Causes of canker sores vs. cold sores

Cold sores are caused by a virus. Canker sores aren’t.

Canker sores are usually triggered by:

• Stress
• Minor mouth injuries, like accidentally biting your cheek
• Certain foods, especially citrus fruits and tomatoes
• Medications, like ibuprofen or other NSAIDs
• Vitamin deficiencies, including B12, iron, folate or zinc

“Stress plays a big role,” Dr. Fernandez notes. “We tend to see more canker sores during periods of emotional or physical strain.”

Cold sores, on the other hand, are caused by herpes simplex virus type 1 (HSV-1) — sometimes called “oral herpes.” It’s a very contagious virus that spreads through close contact.

You can get HSV-1 by:

• Kissing someone with an active cold sore
• Sharing drinks, lip balm or eating utensils
• Touching the sore and then touching your own mouth

It’s also possible — though less likely — to spread the virus even when you can’t see a sore. That’s called asymptomatic shedding.

Once you have the virus, it stays in your body and can reactivate, especially when triggered by:

• Stress
• Sun exposure
• Hormonal changes
• Illness or fever

“Stress lowers your immune system’s ability to suppress the cold sore virus, which can lead to an outbreak,” Dr. Fernandez explains. “Sunlight is another big one — UV rays can reactivate HSV-1 in people who’ve had cold sores before.”

Treatment differences

Both canker sores and cold sores usually heal on their own, but treatment can help ease your pain and shorten the healing time. And while canker sores can’t spread from one person to another, cold sores can. So, getting appropriate treatment for cold sores can help stop the spread.

Canker sores often go away within one to two weeks. To feel better faster:

• Rinse with warm salt water. Mix 1 teaspoon of salt into a 1/2 cup to 1 cup of warm water. Swish and spit — don’t swallow. “It’s a simple, effective way to calm inflammation and ease pain,” Dr. Fernandez advises.
• Avoid acidic, spicy or crunchy foods. These can make the sore worse or more painful.
• Use over-the-counter numbing gels or mouth rinses. These can reduce pain while the sore heals.
• Watch for patterns. If you get frequent canker sores, keeping a symptom journal can help identify triggers.

Cold sores also last about a week or two, but you can take these steps to reduce pain and speed healing:

• Apply ice or a cold compress. This can help reduce swelling and discomfort.
• Use a topical antiviral cream (like Abreva®). Best if applied at the first sign of tingling.
• Try numbing agents. Products with lidocaine or benzocaine can help ease the pain.
• Ask your doctor about antiviral medications. Prescription pills may shorten the duration or prevent frequent outbreaks.
• Protect your lips from the sun. “Use a lip balm with SPF 30 or higher if you’ve had cold sores in the past,” Dr. Fernandez recommends.

During an active outbreak, avoid kissing, sharing items or touching the sore — and wash your hands often.

Seeking help

If you’re not sure if you’re dealing with a canker sore or cold sore, don’t guess — check with a dermatologist or a primary care provider. Also seek medical attention if:

• Your sore lasts more than two weeks.
• You get frequent or severe flare-ups.
• The pain interferes with eating, drinking or speaking.
• You notice other symptoms, like fever, fatigue or swollen lymph nodes.

A healthcare provider can help determine whether it’s a canker sore, a cold sore or something else — and recommend the right treatment based on your symptoms. They can help you find relief and prevent future flare-ups.