What Are Mouth Ulcers?

Answer:

Canker sores are among the most common causes of painful sores in the mouth. They aren’t contagious and are not the same as cold sores (fever blisters), which occur on the outer lip.

The cause is unknown, but the condition is suspected to result from a reaction of the immune system. Additional causes may include: bacterial infections; hormonal disorders; stress; trauma; some medications; allergies or sensitivities; toothpastes containing sodium lauryl sulphate; and deficiencies of iron, folic acid, or vitamin B12.