Is It a Canker Sore or a Cold Sore? A Visual Guide to Help You Tell the Difference

A mouth sore can make it hard to eat, drink, brush your teeth, and sometimes even talk. They can also be embarrassing, especially when they show up on the outside of your lips. But are they really a serious problem?

Most mouth sores are either cold sores or canker sores. While these names might sound pretty similar, the distinction between them is important. Let’s take a closer look at the difference between cold sores and canker sores, and what to do if you think you have one.

What are cold sores (oral herpes)?

Cold sores (also called fever blisters) are painful blisters caused by the herpes simplex virus (HSV). They usually appear on (or around) the lips, but they can sometimes happen inside the mouth and on the tongue. 

Symptoms include:

• Burning, tingling, or itching skin

• A cluster of fluid-filled blisters that break open and crust over

• Fever, tiredness, or muscle aches are possible (especially with the first outbreak)

What are canker sores?

Canker sores are small, painful ulcers (sores) that can happen for many different reasons. They usually appear on the inside of the lips and cheeks, on the tongue, and the roof of the mouth. 

Symptoms include: 

• Sometimes, a burning or tingling sensation

• One (sometimes more) small painful bump that develops into a round, open sore

• Sore with a white or yellow center and a red border

• Can turn gray as it heals

Pictures of canker sores vs. cold sores

Here are some pictures that show some of the differences between canker sores and cold sores. The differences to look for are summarized in the table below.

A typical canker sore appears on the inner lower lip.

A cold sore on the lower lip is crusted over.

Three canker sores show up on the tongue.

Cold sore blisters on the lip.

Understanding the differences between canker sores and cold sores

Canker sores and cold sores can look and feel similar, but they’re not caused by the same things, and they don’t behave the same way. Here’s how they differ. 

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• Eating with canker sores: Learn which foods are less likely to cause pain if you have canker sores.

1. Causes

Understanding the difference between canker sores and cold sores begins with knowing a bit about what causes them.

Cold sores are caused by the herpes simplex virus (oral herpes)

Cold sores are a symptom of oral herpes. That can sound alarming, but oral herpes is different from genital herpes. Most cold sores are caused by HSV-1, and more than half of U.S. adults carry this virus. Once you have HSV-1, it stays in your body and can flare up from time to time.

Canker sores have many causes

Unlike cold sores, canker sores aren't caused by HSV. They have a long list of possible causes, including:

• Viral infections like coxsackie virus (which causes hand, foot, and mouth disease), cytomegalovirus (CMV), or the human immunodeficiency virus (HIV)

• Stress, or feeling run down

• Injury or trauma like after biting the inside of your cheek; or for babies, during teething or after a toy-related injury

• Autoimmune disorders such as celiac disease or systemic lupus erythematosus 

• Nutritional deficiencies like low levels of iron, folate, vitamin C, or vitamin B12

• Bacterial or fungal infections such as syphilis, tuberculosis, or Valley fever

• Hormonal changes such as those related to your menstrual cycle

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With so many different causes, it’s likely that everyone gets canker sores at some point — and most of the time we never know what causes them. A single canker sore, or a single group of canker sores, that comes and goes within 1 to 2 weeks usually isn’t a big deal.

2. Location

You can often tell the difference between cold sores and canker sores based on where they show up.

A cold sore (oral herpes) is usually a group of blisters or crusts on the lip 

A typical cold sore starts as a group of blisters on the outside surface of your lip. Over a couple of days, they grow larger, break, and turn into an open sore. Then they crust over and heal. The whole process takes a couple of weeks.

But there’s one important note: If you’ve never had HSV-1, you might have a different experience when you get it for the first time. A new infection with HSV-1 can sometimes cause herpes gingivostomatitis. This is a condition that comes with a fever and dozens of painful sores inside the mouth, across the tongue, and on the gums. 

Canker sores can happen inside the mouth or nose

Canker sores aren’t as predictable as cold sores. They can show up anywhere on your mucous membranes — that is, anywhere on the moist, pink skin inside your mouth or nose. 

Canker sores often start out as a single small ulcer, although this depends on the cause. Over a few hours or days, they can grow larger and more painful, and more ulcers can appear nearby. 

3. Pattern

Another important piece in understanding mouth sores is when they occur.

Cold sores tend to come back during times of stress

If you’re a person who gets cold sores, you’ll find they pop up during times of stress — and not just psychological stress. Anything that stresses your body, from illness to ultraviolet (UV) sunlight exposure, can trigger a cold sore.

This happens because HSV never goes away completely. Instead, it hides deep inside your nerve cells, where it can stay for years without causing problems. It reemerges when you’re most vulnerable.

Many canker sores are isolated, but they can return in a pattern

Anyone can get a one-off canker sore or even a group of canker sores that appears and then fades over time. This is the case for most people. 

But some people tend to get recurring canker sores, over and over again. This is typical with certain medical conditions, like:

• Cyclic neutropenia

• Periodic fever, aphthous stomatitis, pharyngitis, adenitis syndrome (PFAPA)

• Crohn’s disease

• Behçet’s disease

• Celiac disease

In these cases, canker sores also tend to come on during times of stress. But unlike cold sores, recurring canker sores often come with other symptoms, like fevers, joint pain, or rashes. 

If you tend to get mouth sores over and over again, it’s worth talking with a healthcare professional. Sometimes blood work or other tests are needed to figure out what’s going on.

4. Whether they’re contagious 

When you have a mouth sore, the last thing you want to do is spread it to others — especially if it can cause problems.

Cold sores are very contagious, and HSV can be dangerous

HSV, the virus that causes cold sores, can spread between people very easily. It spreads fastest when you have an open sore — that is, after the blister has broken open and before a crust has formed over it. But it can spread any time you have symptoms (even before the blisters develop). 

Although HSV isn’t usually dangerous for healthy adults, it can be a major problem for some people. In particular, HSV can cause life-threatening infections in:

• Newborns

• Older adults

• People who are immunocompromised or who have weakened immune systems

Anyone with a cold sore should stay away from vulnerable individuals, including people who are pregnant and near to term.

Canker sores can be painful, but usually they are not contagious or dangerous

Most of the time canker sores aren’t contagious. Even when they’re linked to an infection, they don’t tend to be a major source of germ spreading.

That isn’t to say canker sores aren’t a big deal. They can be very painful. And sometimes they can be a sign that something else is going on, especially when they keep coming back.

Treatment for canker sores vs. cold sores

Although both types of mouth sores might call for pain control, the way you’ll want to handle them is quite different.

Treat cold sores with antiviral medication if you catch them quickly

Many people feel a tingling or burning on the lip before a cold sore appears. That early warning matters — antiviral treatment works best if you start it right away.

Over-the-counter options

Here are some over-the-counter (OTC) choices for treating a cold sore:

• Docosanol (Abreva), an OTC antiviral cream you apply five times a day at the first sign of symptoms.

• Zinc oxide or zinc sulfate, when applied to the cold sore may shorten healing time.

• Benzocaine (Orajel), can numb pain but won't treat the virus itself.

Prescription options

And here are some prescription options:

• Acyclovir (Zovirax)

• Valacyclovir (Valtrex)

• Famciclovir (Famvir)

These are antiviral medications that you take by mouth, as pills. They are very effective against HSV-1 when you start them early. If you get cold sores often, talk with a healthcare professional about keeping medication on hand — or taking a daily antiviral to prevent cold sores.

For canker sores, focus on pain relief

There’s no single medication that makes canker sores disappear faster. Treatment is mostly about easing discomfort until the sore heals on its own.

OTC options

Here are some OTC options for treating canker sores:

• Pain relievers, like Acetaminophen (Tylenol), ibuprofen (Advil or Motrin), or naproxen (Aleve)

• Benzocaine oral gels (Anbesol, Orajel, Zilactin-B)

• Hydrogen peroxide rinses (Orajel, Peroxyl)

Home remedies

There are home remedies for treating canker sores too, including:

• Alum (potassium sulfate) powder, used as a paste

• Saltwater or baking soda rinses

• Honey or milk of magnesia applied with a cotton swab

Prescription options

In severe or persistent cases, prescription treatments like topical or even oral steroids may help reduce pain and inflammation.

Frequently asked questions

Why trust our experts?

Written by:

Kerry R. McGee, MD, FAAP

Kerry McGee, MD, FAAP, has over a decade of experience caring for babies, children, and teenagers as a primary care pediatrician. She has a special interest in adolescent health, particularly in adolescent mental health.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. A pulmonologist and hospitalist, she practiced and taught clinical medicine at hospitals in London for a decade before entering a career in health education and technology.

Reviewed by:

Maria Robinson, MD, MBA

Maria Robinson, MD, MBA, is a board-certified dermatologist and dermatopathologist who has practiced dermatology and dermatopathology for over 10 years across private practice, academic, and telehealth settings. She is a fellow of the American Academy of Dermatology and the American Society of Dermatopathology.

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