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How to Tell the Difference Between a Cold Sore and a Canker Sore

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Looking in the mirror and suddenly seeing a blemish that wasn’t there a day ago can be a pretty intense experience, especially if you think the blemish might be a cold sore or a canker sore but can’t exactly tell which.

If you’ve found yourself in this exact situation, don’t worry! There are quick ways to tell the difference between a cold sore and a canker sore, and good news — they’re both easy to treat.

First, let’s start with the basics. Canker sores and cold sores are both types of mouth sores — and can be painful and aggravating to deal with. However, they are two very different entities.

What Is a Canker Sore?

According to Hadley King, MD, a board-certified dermatologist in New York City, canker sores appear on moist surfaces of your mouth, on the inner cheek and lips as well as the side of the tongue. They are typically small to large round or oval shallow ulcers. Canker sores tend to be painful, with larger ones often taking longer to heal. They may appear whitish or yellowish with a red border.

According to Lillian SooHoo, MD, a board-certified dermatologist at The Menkes Clinic in Mountain View, CA., a canker sore can last up to several weeks and can be brought on by trauma, such as eating sharp potato chips, aggressive tooth-brushing, or orthodontic braces and wires rubbing against the inner cheek. Other triggers for canker sores include diseases of the immune system and vitamin deficiencies. Canker sores are not contagious.

“If the source of the trauma isn’t removed, painful canker sores can become a persistent cause of discomfort inside the mouth,” SooHoo says. “Otherwise, canker sores usually take a few weeks to heal.”

What Is a Cold Sore?

Cold sores, on the other hand, are small blisters filled with fluid on a red base. They usually occur on the outside of the mouth, on the dry surface of the lips, and sometimes even on the face. Cold sores usually form on or around the lips, but in some cases they may also form inside the mouth. They are caused by reactivation of the herpes simplex virus (types 1 or 2). “Most people can tell when a cold sore is coming on, as burning, itching and/or a tingling sensation happens before the actual sore appears,” King said.

While you typically have to wait for a canker sore to heal on its own, you can get rid of your cold sore in two and a half days1 with an antiviral topical cream such as Abreva, which is available over the counter. When you feel that tingle coming on, nothing heals a cold sore faster2.

Cold sore symptoms will vary, depending on whether it is your first outbreak and you are experiencing with a new HSV infection, or if you have had the virus for a while and are experiencing a flare, King says. If it's a primary outbreak, the symptoms are generally more severe: burning and tingling followed by painful sores, fever, body aches, headache, or swollen lymph nodes. If it's a flare-up of an old infection, the symptoms usually begin with a burning, tingling, or itching sensation, followed by development of the cold sore. The cold sore will then crust over and heal in one to two weeks.

A key difference between cold sores and canker sores is that cold sores are contagious, as they are caused by a virus. Any contact with the sore or saliva from an infected person through kissing, sharing food and drinks, sharing towels, etc., can transmit the virus to other people.

1 When used at the first sign. Median healing time 41. days, 25% healed in 2.5 days
2 Among OTC cold sore medications