What Causes Canker Sores?

The exact cause of Canker Sores is still unclear, but one theory is that they result from excessive immune system activity that occurs in response to tissue or mucosal inflammation.  

Many canker sores likely start with a small insult to the mucous membrane lining inside the mouth.  Immune system responses engaged to heal the tissue may instead increase damage to the area through over activity.  As the damaged area grows, secondary infection with bacteria may worsen the situation by causing the sore to grow directly and through further immune system stimulation.  

This theory is consistent with observations of increased rates in individuals under stress, and those with particular immune system genetics conferring increased auto-inflammatory risk.  Almost 30% of cases are attributed to family history.