Are Canker Sores Contagious?

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Canker sores are unpleasant in sight and feel. But you might be wondering if they're contagious or not. This lesson explains how they are not and compares canker sores to other similar sores you may see in and around your mouth.

Sores Around the Mouth

Have you ever had a sore around your mouth? How about inside of the mouth? Did you know that while many of them may look the same they are not necessarily related? Some of them may be caused by viruses, some may be an indication of cancer, and some occur for no known reason. One kind of sore, known as a canker sore, is sometimes mistaken for the others and is believed to be contagious. But is it? Simply put no, but let's find out why.

A canker sore inside of the mouth.
Canker sore

What are Canker Sores?

If you ever see a sore in or around your mouth, you might be wondering: What is it? Is it contagious? Is it cancer? Luckily, canker sores are pretty distinct.

  • They occur inside of the mouth. This is unlike cold sores (fever blisters), which most often occur around the lip margin. Meaning, cold sores occur outside of the oral cavity (the inside of the mouth), while canker sores occur inside of the mouth.
  • Canker sores are usually small and round ulcers that have a whitish center with a reddish border. This is unlike a completely red sore that may have been the result of you biting on the inside of your lip too hard by accident.
  • Canker sores are typically painful although the pain usually subsides within a week. Compare this to some forms of mouth cancer. Like canker sores, they may initially appear small and even white in color. However, unlike canker sores, some of the cancers of the mouth start off painlessly but become painful with time. This is the opposite of what happens with canker sores.

Remember, these are just very general guidelines, as some forms of mouth cancer can be red in color or painful right off of the bat. So if you're not sure what it is that you're looking at, always see a doctor immediately.

Why Aren't Canker Sores Contagious?

Despite the pain and nasty look to them, canker sores do have one upside. Unlike cold sores, which are caused by a herpes virus, canker sores are not contagious. No one knows for sure what causes canker sores. It may be sensitivities to food, chemicals found in mouthwash, diseases of the intestinal tract, or even stress. However, even if some of them may be tied to being caused by some forms of bacteria (this is disputed), there is no evidence that they are contagious to other people. So if you see one in your mouth, fear not of kissing your loved one or talking when standing really close to them. Unlike a cold, flu, or herpes, you can't pass these guys on to anyone you meet.

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