Except in a few cases where there is a clear reason such as an underlying disease or a vitamin deficiency that has shown up in blood tests - the answer to the question of what causes canker sores is pretty much unknown.
Millions of people around the world suffer from them and sure - in few rare cases your doctor will find that you have some immune system problem or an allergy to gluten or wheat (celiac disease) - but for the vast majority of us there is simply no cause to be found.
Watch the video below for more information and canker sore support.
Some well recognised causes of canker sores include:
+++ Eating too many salty potato snacks
+++ High levels of stress or lack of sleep
+++ Vitamin B deficiency
+++ Drinking too many acidic fruit drinks like fresh orange or grapefruit juice
+++ Not enough iron or folic acid in the diet
+++ A shortage of zinc - and zinc supplements often help to improve things for chronic sufferers