turth is there is no exact known cause for mouth ulcers a.k.a
canker sore... could be multiple things like vitamin deficiency,
the tooth paste you're using or an accedental cut... someone else
who have the same diet as you may not get canker sore...
Still advise bonjella, or if ya want or traditional stuff, honey,
drink lotsa water and fruits and vegetable to heal up the wound...
and obviously don't agravate it by eating spicy food... it also
maybe caused by your tooth paste... though unlikey, ya may wanna
change your tooth paste...
In the end, still a mystery.....