This will sound really kookoo, but I too was plagued with canker sores from the time I was a toddler until a few years ago, when I gave up eating dairy foods. They were always worse just before my period, and sometimes I'd have 5 or 6 in my mouth at the same time, making it almost impossible to eat and talk. Twice I had to see a doctor for canker sores: one on my lip that had turned black - ugh, and another in my throat that I thought might be cancer! They would settle into strange places, up on the underneath of my palate, on my tongue. These were the worst: they'd slide against my teeth - OUCH!!!

I gave up dairy because I had a test that showed I was lactose intolerant, and the Lactaid supplements didn't seem to be helping. Now, on the rare occasions when I cheat (i.e. Christmas Day) and have a small amount of dairy, I usually notice the start of a canker sore within 24 hours, which simply "dies" the next day without ever breaking into ulcer mode. This is probably not the cause for everyone, but for me, it's the answer.