What are possible causes of recurrent canker sores?

Triggers: Have been identified/linked & not really causes. It is multi-factorial, but some triggers include: food allergies, nutritional deficiencies (b12, folic acid, vit. C), emotional stress, smoking, dental appliances, other autoimmune illnesses (bechet's, lupus, crohn's), menstruation, hormone therapy, pregnancy. Some studies have linked toothpastes containing sodium lauryl sulfate.