What is the difference between cold sores and canker sores?

Canker sores are small ulcers with a white or gray base and a red border; canker sores appear inside the mouth. They are not contagious, but can return frequently and may be only one canker sore or several. Their exact cause is uncertain but some experts believe that immune system problems, bacteria or viruses may be involved. Canker sores usually heal on their own after a week or two.

Cold sores are groups of fluid-filled blisters that often erupt around the lips and sometimes under the nose or around the chin. Cold sores are caused by the herpes simplex virus type 1 and are very contagious. The initial infection (primary herpes) may be confused with a cold or flu and can cause painful lesions to erupt throughout the mouth. Once a person is infected with primary herpes, the virus stays in the body and causes occasional attacks. Cold sore blisters usually heal in a week by themselves.
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Fever blisters or cold sores, are caused by the herpes simplex virus, and are commonly mistaken as canker sores. The difference between a cold sore and a canker sore (apthous ulcer) lies in their cause and location.

Cold sores are caused by the virus Herpes simplex and  may occur inside or outside the mouth, as well as on the chin or in the nostrils, and they often come back in the same location. They can be spread by mouth-to-mouth contact, with kissing being the most likely cause of spread.

Canker sores are not caused by a virus and are not spread by kissing and only develop on the inside of the mouth. While both fever blisters and canker sores might look the same with a reddish and inflamed appearance, canker sores might also appear white and usually do not bleed.

Many people confuse cold sores with canker sores. While cold sores, or oral herpes, can sometimes develop in the mouth, cold sores are the result of the herpes simplex virus and canker sores are ulcers that form in the mouth tissue. Unlike cold sores, canker sores are not contagious.

Continue Learning about Canker Sores

Canker Sores

Canker Sores

Aphthous stomatitis is a sore that forms inside the mouth, and the most common type is a canker sore. These sores, also called mouth ulcers, are yellow-gray with red rings around them and usually heal in a week or two. Sometimes c...

anker sores are larger or occur in clusters and can take over a month to heal. Treatment is usually with an oral antiseptic and analgesic. Learn more about what affects your risk for canker sores with expert advice from Sharecare.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.