Cold sores and canker sores: What's the difference?

Mar 4, 2017

Whether caused by infection, injury, or stress, cold sores and canker sores are a common occurrence for many of us. Undoubtedly, they’re both very irritating, but is there a difference between the two? To find out, “Take Care” spoke with Dr. Mark Burhenne, a tenured dentist and the expert behind the popular website, “Ask the Dentist: Oral Health for Total Wellness.”

Cold sores and canker sores are entirely different conditions. The simplest way to differentiate between cold sores and canker sores is by location, says Burhenne. Cold sores are always on the outside of the mouth, typically directly on the lips, whereas canker sores are always on the inside. This is due to the different nature of the causes.

Cold sore
Credit AJC1 / Flickr

Cold sores, Burhenne explains, are caused by a viral infection in the body. The infection, known as herpes simplex one, can remain dormant for extended periods of time, but will result in a fluid-filled blister when triggered. Various factors can elicit a cold sore, including cold, dry weather, and chapped lips. And they’re very common, with 80 to 90 percent of us coming in contact with herpes simplex one by age six or seven. However, Burhenne notes that even if the body has come into contact with the virus, some individuals’ immune systems may be able to keep a cold sore at bay. 

Canker sores on the other hand, while arguably just as painful as cold sores, have no viral component and are typically the result of some sort of mechanical trauma. Biting the inside of your cheek, for example, could wind up as a canker sore as the body tries to heal the wound. Similarly, other factors such as fatigue, poor diet, and hormone fluctuations can lead to a sore in the mouth. Many of us have likely bit the same spot inside our mouth so many times, it can feel like the sore is lasting forever. And rightly so, because canker sores usually have 14 to 18 day duration, says Burhenne.  

Another big difference is the contagion factor. Because canker sores are caused by some physical trauma in the individual as opposed to a viral infection with cold sores, they are not contagious. But cold sores, which come from the herpes simplex one virus, are highly transmittable. So much so, that according to Burhenne, dentists typically don’t want to see patients when they have a cold sore, to prevent spreading the virus around the dentists’ office.

So what do you do if you have either of these sores? Burhenne notes that the different treatments for both are palliative, meaning they don’t address the cause. For canker sores, he recommends flushing out the mouth with a saturated salt water solution, and for cold sores, there are pills and creams on the market. The medications however, are unfortunately very expensive. A single three gram tube of anti-viral cold sore cream can cost $600 to $800.

But if you sense a cold sore coming, your dentist can help you get your hands on the medicated cream, Burhenne says. Before the sore emerges, the infected area will begin to tingle, and if you can catch it early, the anti-viral cream may be able to keep the cold sore below the surface. Fortunately, both sores are nuisances more than anything and don’t threaten the health of the individual, but nevertheless they are quite a bother, so talk to your dentist if you are seeking more advice on moving forward with treatment for a cold or canker sore.