Canker Sores vs. Cold Sores—What’s the Difference?

Canker sores, cold sores, fever blisters. Call them what you will, mouth sores are painful. There’s no denying that they can be unsightly and make mealtimes an uncomfortable experience.


Did you know, however, that canker sores and cold sores are two very different problems? Understanding their differences is the key to helping them heal as quickly as possible and getting back to your normal life.

What Makes Cold Sores and Canker Sores Different?

Canker sores are also called aphthous ulcer and to this day no one can say for sure what causes them. They seem to show up in response to a variety of irritants and triggers including:


  • Trauma (like biting your lip)
  • Spicy foods
  • Alcohol
  • Stress
  • Fatigue
  • Hormone changes
  • Toothpaste allergy


Cold sores, or fever blisters, on the other hand, are quite specifically caused by a viral infection. Once you catch the very common and highly contagious herpes simplex virus, the infection will flare up in the form of cold sores. Outbreaks are sparked by things like stress, sun exposure, or a weakened immune system.


So the main difference between cold sores and canker sores is their origin: cold sores are viral while canker sores have an unknown cause.


How do you know whether you have a cold sore or canker sore? It’s actually quite simple to tell them apart.

How Canker Sores and Cold Sores Look Different

A canker sore will have a clearly defined border. It usually presents as just one isolated lesion that has a red ring surrounding a pale yellow- or gray-colored patch of tissue. It is possible to get more than one canker sore at one time, but they don’t typically show up in multiples.


Cold sores start out as a cluster of tiny clear fluid-filled vesicles on one patch of skin. They eventually turn cloudy and then rupture, forming a shiny scab-like crust.

Location Is Everything

Another key detail that will help you distinguish a cold sore from a canker sore is the location since they show up in very different places.


Cold sores happen outside the mouth on dry skin. They may develop on the corner of the mouth, edge of the lip, around the nose, or even on the cheeks. In rare and dangerous cases, cold sores can form in the eye. They typically recur near the same place with each outbreak.


Cankers form on the soft tissue inside the mouth. This can include the back of the throat, insides of the cheeks, the side of the tongue, the floor of the mouth, and inside the lip. Almost any tissue inside the mouth that isn’t attached to your gums or palate has the potential to develop a canker sore.


So in general, a painful lesion on the outside of your mouth is likely to be a cold sore while one inside your mouth is probably a canker sore.

How Do You Treat Cold Sores and Canker Sores?

It’s important to remember that because cold sores are caused by a virus they can’t technically be “cured” any more than you can cure a common cold. Even so, you can reduce your discomfort and speed up healing by:


  • Applying a topical antiviral cream as a doctor directs
  • Keeping the sore clean and free of makeup
  • Softening the sore with a cool moist cloth to prevent painful crusting


The cold sore virus is also extremely contagious. Be mindful of not sharing your cosmetics or food utensils with others or kissing others around the time of a cold sore outbreak.


But if all you have is a canker sore then you don’t need to worry about sharing it; cankers aren’t contagious.


To get relief from a canker sore, try swishing with a cleansing rinse. A 1:1 ratio of water and hydrogen peroxide may help. Warm salt water can be particularly soothing. There are topical oral pain relief gels you can apply for instant relief.


In the meantime, avoid hot, spicy, crunchy, or acidic foods to let the canker heal. You might also try switching to a natural toothpaste to see if that calms down a possible allergic reaction.

Medical Help for Cold Sores and Canker Sores

How do you know if you have a cold sore? It will be a cluster of blisters or an oozing crust on the skin outside your mouth. And if you have a canker sore? The lesion will be ringed in red and located inside your mouth.


But what if you still aren’t sure? Your local dentist (a mouth health specialist, after all!) may be your best resource.


Visit the dentist as quickly as possible to get an accurate diagnosis for your mouth sore. The sooner you get professional help, the sooner you can get relief and possibly even prevent another outbreak. Your dentist can recommend a variety of treatments to try and see what works for you.

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