The exact cause of Canker Sores is uncertain. Some experts believe that immune system problems may have potential influences. Other causes can be trauma, allergies, iron and vitamin deficiencies. These sores usually heal on their own in 7 to 10 days. Our office would instruct you on what foods to avoid, over-the-counter medications, or in severe cases prescribe a special mouth rinse to help reduce the painful symptoms of these sores.