Canker Sores And Cold Sores: What’s The Difference?

Do you have a sore on or near your mouth and wonder whether it's a canker or cold sore? These two sores are common in children and adults and are sometimes confusing. 

Canker sores and cold sores are two different medical issues, but the terms are often used interchangeably. They are both painful mouth sores, which explains the confusion.

This post explains the significant differences between a canker sore and a cold sore. 

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What are cold sores?

Cold sores, also known as fever blisters, appear on or around the lips. Sometimes, the blisters may form inside the mouth. The sores often appear as a cluster of blisters, and sometimes they eventually burst, causing oozing and crusting. 

Despite its name, it is not related to a cold, but before a cold sore appears, you might experience some cold-like symptoms, such as fever and muscle aches. You will likely also experience a tingling feeling in the mouth area where the sore will appear. Cold sores are caused by a herpes simplex virus (HSV) infection and take about 2–3 weeks to heal. 

What are canker sores?

Canker sores also called aphthous ulcers or mouth ulcers, are white or gray lesions surrounded by a red, inflamed area. The painful sores form inside the mouth, on the tongue, or inside the cheeks or lips. 

Some experts¹ estimate the prevalence of canker sores to be one in 10 people. Moreover, canker sores are more common in women than in men.

There are three main medically known forms of canker sores:

  • Minor aphthous stomatitis: They are under 1cm in diameter and often heal within a week. Also, they do not cause scars.

  • Major aphthous stomatitis: They are larger than 1cm in diameter and often last more than a couple of weeks. This type may leave scarring.

  • Herpetiform aphthous stomatitis: These are clusters of tiny sores (10–100) that may merge to form a large sore. They are the least common and often take 1–2 weeks to heal.

Is it a cold sore or a canker sore?

People often confuse a cold sore and a canker sore because they all form in or around the buccal cavity. However, it's quite easy to tell the difference between a cold sore vs. a canker sore.

The appearance, causes, and symptoms can help you distinguish between a cold sore and a canker sore. Let's find out the differences.

How to identify cold sores vs. canker sores

You can tell the difference between a cold sore and a canker sore based on the location of the blisters. For instance, canker sores only form inside the mouth. Common areas include:

  • Inside the cheeks or lips

  • On your gums

  • Soft palate

  • On or below your tongue

On the other hand, cold sores form on the outside of the mouth, on the lips, corner of the lips, or just above or below the lips.

Before a cold sore form, you may experience a tingling or itching feeling in the area, followed by tiny, fluid-filled blisters that are red with tiny whitish heads. 

Canker sores are typically oval or round in shape. They appear to be yellow or white and may have a red border.

Canker sores vary in size, and the large or major canker sores are painful and take longer to heal.

What causes canker sores and cold sores?

Cold sores and canker sores follow different patterns over time. The causes can also help you identify the difference between the two types of lesions. 

Cold sore causes

Herpes simplex virus, or HSV, is the most common cause of cold sores. Cold sores are mainly caused by the subtype HSV-1 strain. However, the HSV-2 strain can also cause cold sores, though less commonly. 

HSV is very contagious, especially with oozing cold sores. But it can also be contagious when the sores are not visible, for example, when the area starts tingling. The infection mainly spreads through oral contact or items that have come in contact with an infected person's saliva.

Examples include:

  • Kissing

  • Oral sex

  • Sharing utensils

  • Sharing personal items like handkerchiefs or toothbrushes

Canker sore causes

The exact cause of canker sores is still unclear. But according to the American Academy of Oral Medicine² (AAOM), canker sores can be a sign of other conditions, such as gastrointestinal disease. They may stem from an immune system malfunction causing white blood cells to attack the mouth's mucosal cells.

The blisters also may form an allergic reaction to certain foods, mouthwash, or toothpaste. However, canker sores aren't contagious. 

Cold sore vs. canker sore risk factors 

Cold sore risk factors

Most people are at risk of developing a cold sore as it is estimated that 60–70%³ of the world’s population may be carrying the HSV-1. However, not everyone will develop cold sores, other symptoms, or complications. The following may increase the risk of this happening: 

  • Sun exposure

  • Infection, cold, or fever

  • Severe burns

  • A weakened immune system/HIV/AIDS

  • Chemotherapy

  • Eczema

  • Dental work

  • Injury to the site

Canker sore risk factors

  • Stress

  • Injury or tissue damage due to sports accident, dental work, or accidentally biting the lip

  • Eating acidic or spicy foods

  • Poor oral hygiene causes bacterial growth

  • Hormonal level changes

  • A weakened or overactive immune system

  • Frequent use of non-steroidal antiinflammatories 

  • Iron, thiamine, vitamin B12, or vitamin D deficiency

  • Helicobacter pylori bacteria

  • Gastrointestinal issues such as celiac or Crohn's disease

  • Exposure to toxins (e.g., nitrates in drinking water)

Symptoms of canker sores and cold sores

Canker sores and cold sores have some similarities and differences in symptoms. Here are the common symptoms of the two lesions.

Canker sores symptoms

  • Painful sores inside the mouth

  • A burning or tingling sensation

  • Gray, white, or yellow ulcers with a red border

In severe cases, they may cause fever, fatigue, or swollen lymph nodes. 

Cold sore symptoms

Cold sore symptoms follow a five-step pattern:

  • First, you may experience a burning, itching, or stinging sensation around the mouth or where the sore will appear.

  • Second, a fluid-filled blister develops, which is a cold sore. This happens 24-48 hours from the initial tingling sensation.

  • The blister breaks or oozes.

  • It crusts over.

  • Then it enters the healing stage.

When to see a doctor? 

In most cases, both sores heal on their own with no need to see your doctor. You may ask your pharmacist for help with over-the-counter treatments for the symptoms.

They can also offer you antiviral creams in the case of cold sores, which, if used as soon as the tingling or itching sensation starts in the area, are considered more effective in controlling the symptoms and healing time of cold sores.

However, if your symptoms don’t improve, your ulcers don’t start healing after ten days, or you have been experiencing frequent and recurrent ulcers, then it is important to book an appointment with your doctor.

Your doctor will examine your medical history and perform a physical exam to identify if you have a cold sore, canker sore, or something else.

For cold sores, a sample may be taken from the sore to test for HSV. Moreover, the doctor may perform blood tests and other examinations to investigate the possibility of other underlying health conditions, nutritional deficiencies, immune system issues, or food allergies that may trigger these sores.

How to treat cold sores and canker sores

You may not need treatment for small canker sores, as the blisters may disappear within a week or two on their own. However, if you have large canker sores that are painful or long-lasting, there are various treatment options, including:

  • Oral medications like steroids

  • Prescription mouthwashes that contain dexamethasone

  • Cautery — using an instrument or chemical to burn or destroy the sore

  • Over-the-counter gels and creams

  • Supplements for any nutritional deficiencies

  • Treatment of any underlying triggering condition, if found

Cold sores also go away on their own and typically don't require treatment. However, you can ease symptoms and accelerate the healing process using:

  • OTC gels and creams

  • OTC antiviral creams

  • Prescription antiviral drugs

The lowdown

Cold sores and canker sores are often used interchangeably to refer to blisters in or around the buccal cavity. However, there are some notable differences between the two conditions based on the causes, symptoms, and location of the sore. 

While the two types of sores often go away on their own, some treatments, like over-the-counter medication, can help speed up the recovery process.


What causes canker sores in the mouth?

The exact cause of canker sores is still unclear. However, the sores can be triggered by nutrient deficiencies, stress, and hormonal fluctuations, among other risk factors.

Can you kiss if you have a canker sore?

Yes, canker sores are not contagious. Therefore, you can kiss without passing them on to your partner.

Can you kiss me if you have a cold sore?

No, cold sores are highly contagious. You should avoid any oral contact from the moment you start feeling a tingling or itching sensation in the area, even before the sore appears — this also includes avoiding any oral sex.

  1. Canker sores (mouth ulcers): Overview (2006)

  2. Canker sores | American Academy of Oral Medicine

  3. Herpes simplex virus | World Health Organization

Other sources:

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