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Canker Sore Vs. Cold Sore: Spot These 3 Differences

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Medically Reviewed By Colgate Global Scientific Communications

If you've ever had a sore on or near your mouth, you've likely thought to yourself: Is this a canker sore or a cold sore, and what's the difference? Here are three significant differences of a canker sore vs. cold sore to help you determine your next steps for treatment.

1. Appearance

The first way to differentiate a canker sore vs. cold sore is by appearance. As the Mayo Clinic explains, canker sores — also called aphthous ulcers — appear inside the mouth. They develop in soft tissues, such as in the cheeks, gums, under the tongue or on the tongue. Canker sores look like small white or yellow circles surrounded by a red border and may cause discomfort when you eat or drink.

Cold sores, on the other hand, usually appear on or around the lip, as the Mayo Clinic explains. A cold sore often looks like a cluster of blisters, and they can eventually burst, causing oozing and crusting.

2. Causes

Canker sores and cold sores have different underlying causes. According to the American Dental Association, the exact cause of canker sores is unknown. Experts speculate that they may happen as a result of immune issues, mouth trauma, bacteria or viruses.

Cold sores result directly from the herpes simplex virus (HSV-1), according to the Mayo Clinic. This virus is dormant until triggered, which is when you might experience a tingling or burning sensation in your mouth and the development of a sore. Several factors can trigger the recurrence of a cold sore:

  • Stress
  • Other viral infections
  • Fatigue
  • Exposure to sun or wind
  • Hormonal changes
  • Fever

3. Treatments

Both canker sores and cold sores usually heal on their own. Minor canker sores typically take a week or two to heal, according to the Mayo Clinic, while cold sores may take two to four weeks. Cold sores usually do not leave scars; however, major canker sores have the potential to cause scarring.

If your symptoms last longer than you'd like, you can also discuss treatment options with a medical or dental professional. For canker sores, if they are unusually large, clustered or painful, your doctor or dentist may suggest mouthrinses, topical ointments or oral medication.

Because cold sores are caused by HSV-1, the American Academy of Dermatology (AAD) suggests treating them with antiviral topical or oral medications. If you are experiencing discomfort, your doctor or dentist may also prescribe a pain-relief medication. In addition, the AAD strongly encourages the use of sunscreen during an outbreak, as sun exposure can affect the healing of the sore.

Another important note: Unlike canker sores, cold sores are contagious, according to the Mayo Clinic. Therefore, to prevent spreading the virus, you should not share utensils or any other items that touch the mouth.

The easiest way to tell the difference between a canker sore and a cold sore is by its location. If the sore is in your mouth, it's likely a canker sore. If it's outside the mouth, it's probably a cold sore. If you aren't sure — don't worry. See your doctor or dentist so that they can determine what it is and recommend the proper treatment.


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This article is intended to promote understanding of and knowledge about general oral health topics. It is not intended to be a substitute for professional advice, diagnosis or treatment. Always seek the advice of your dentist or other qualified healthcare provider with any questions you may have regarding a medical condition or treatment.

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