Are Canker Sores Contagious?

Good News!  Canker sores are not contagious. No amount of exposure to canker sores will cause the condition to spread from one person to another.  While the exact cause of canker sores is not known, there is no evidence showing canker sores can be spread from one person to another.

Canker sores should not be confused with cold sores:

  • Cold sores occur on the lips, are caused by the herpes virus, and are contagious.
Image of Cold Sore
This is a Cold Sore. Note the sore placement on the lips, rather than the interior of the mouth
  • Canker sores occur inside the mouth, are not caused by a virus, and are Not contagious.

    canker sore on inner lip
    A Canker Sore. Note the ulcer placement in the interior of the mouth.

Canker sores are the result of immune response to certain conditions in the mouth or body, whether that be physical trauma in the mouth, acidic oral conditions, or times of high stress.