Is It a Canker Sore or a Cold Sore?

A canker sore is a whitish or yellowish ulcer that appears inside the mouth. A cold sore (fever blister), in contrast, is caused by the virus herpes simplex virus 1 (HSV-1). HSV-1 lays dormant in your nerve cells after initial infection. If something activates HSV-1, blisters mostly appear outside your mouth, on or near your lips. A cold sore can sometimes develop inside your mouth, typically on the gums or roof of your mouth.

Many people use the terms "canker sores" and "cold sores" interchangeably, but these painful mouth sores are different. Read on to learn how to tell the difference between a canker sore and a cold sore.

How To Identify Cold Sores vs. Canker Sores

One of the main differences between canker sores and cold stores is the location. Canker sores only appear inside your mouth, while cold sores typically appear on the outside.

Some of the main differences between canker sores and cold sores include:

Canker Sores

Canker sores (aphthous ulcers) appear as open sores on the inside of your mouth, usually on the inner parts of your cheeks, lips, or on your tongue. You likely will not find canker sores on the gums, but they may appear at the very base of your gums. Some people notice burning or tingling in their mouth before the ulcer forms.

Canker sores, which often appear in clusters, are usually:

• Small (i.e., one-third of an inch in diameter)
• Painful
• Small bumps inside your mouth that burst after one to two days
• Whitish or yellowish with a red border and then become gray as they heal

Cold Sores

Cold sores (fever blisters) appear outside your mouth, often on the corner of your lip. They can also develop in your nose or eye. Symptoms include:

• Blisters that break quickly, leak fluid, and then crust and scab over
• Fatigue
• Fever
• Itching or tingling in the area up to one day before the ulcer appears
• Pain
• Swollen glands
  

Causes 

Viruses cause cold sores, which are extremely contagious. Canker sores, on the other hand, are not contagious. It's unclear what exactly causes canker sores, but several things may increase your risk.

Canker Sores

No one knows what exactly causes or triggers canker sores, but they are not contagious. Risk factors may include:

• Food allergies
• Hormone changes and menstrual periods
• Nutritional deficiency (e.g., low folic acid, iron, or vitamin B12)
• Physical injury
• Smoking
• Stress
• Viral infection

Cold Sores

The virus HSV-1 causes cold sores. HSV-1, which is very contagious and common, does not go away once you get it. The virus travels up a nerve after the initial infection, where it stays out of sight until something triggers it. HSV-1 will then migrate down the nerve to the mouth, manifesting as a blister.

Cold sore triggers can include:

• Dry, cracked lips
• Hot and cold temperatures
• Menstrual periods
• Other infections
• Stress
• Sun exposure

Diagnosis

A healthcare provider can typically tell the difference between a canker sore and a cold sore by examining the ulcer. See a healthcare provider if you have canker sores that make it hard to eat or drink or last longer than two weeks. They may administer diagnostic tests to check for allergies and herpes infection if you frequently get canker sores.

Canker sores are also sometimes a sign of an underlying health problem like celiac disease. This autoimmune disorder, triggered by gluten (a protein in grains like barley, rye, and wheat), causes damage to the small intestine.

You typically do not need to see a healthcare provider for cold sores. These blisters are generally not harmful unless you have a weak immune system from cancer treatment or another health condition like HIV/AIDS. In those cases, you may require more aggressive treatment, such as a long-term oral antiviral like acyclovir.

Treatment 

Canker sores tend to last a little longer than cold sores. Most canker sores go away within one to three weeks. Cold sores, in contrast, go away within one to two weeks. Both mouth ulcers are typically harmless unless you have an underlying health condition.

Canker Sore

Canker sores mostly go away on their own. You can use an over-the-counter (OTC) pain reliever to alleviate discomfort, usually lasting seven or 10 days.

Other ways to treat a canker sore include:

• Medications: A healthcare provider might prescribe chlorhexidine mouthwash or an oral or topical corticosteroid in severe cases. Gastric acid-reducing drugs sometimes treat pain.
• Milk of Magnesia (magnesium hydroxide): Try rinsing your mouth with a 50/50 mix of Milk of Magnesia and liquid Benadryl. Swish the mixture in your mouth for at least one minute. You may also apply a 50/50 mix of hydrogen peroxide and water and then a dab of Milk of Magnesia to the canker sore. Repeat three to four times per day.
• Mouth rinses: These include saltwater and OTC mouthwashes that do not contain alcohol.

Cold Sore

Most cold sores go away on their own within one to two weeks. You can treat a cold sore at home by applying a cold compress to the blisters or taking an OTC pain reliever. Topical antiviral creams or ointments may lessen pain and quicken healing if applied at the start of an outbreak.

Cold sores can spread to other body parts, so it's important to avoid touching them. Wash your hands if you accidentally touch a cold sore. Make sure you do not touch any other part of your body, especially the eyes. Do not scratch or pick at the blisters, which might cause an infection.

Tips 

Canker sores and cold sores are both painful ulcers that can be bothersome, especially when eating. You can take steps to avoid both canker sores and cold sores, especially if you know what triggers them.

You can prevent canker sores by:

• Brushing your teeth twice per day and flossing daily
• Scheduling regular dental check-ups
• Talking to a healthcare provider about possible food allergies, which might trigger canker sores

Cold sores are contagious and spread easily. You can prevent cold sores by:

• Avoiding triggers if possible (e.g., reducing stress or putting zinc sunscreen on your lips before going outside)
• Not kissing others until the blisters heal completely
• Not sharing straws and lip products or drinking from the same glass as others
• Washing your hands regularly, especially before you touch your eyes

A Quick Review

Both canker and cold sores are common but have different causes, symptoms, and treatments. The exact cause of canker sores is unknown, but HSV-1 causes cold sores. These mouth ulcers can be painful, and both typically go away on their own.

If you have regular or prolonged canker sores, contact a healthcare provider. They can rule out any underlying health problems that may be the cause. Ask a healthcare provider about oral antiviral treatments if you have cold sores and a weak immune system.