Taxman, I have had them as long as I can remember. Both me and my younger brother get them. There are many reasons and possibilities why they form. When I was younger from the ages of 5 years old to my early twenties I got them the most. Sometime I would have up to 6 in my mouth at a time. It was hard to talk let alone eat sometimes. Until the 9th grade I use to chew my nails then I stopped and this seemed to help somewhat although I still chewed on skin on fingers.
Some possible factors that might increase formations of Canker sores:
Not keeping mouth clean enough( lack or not enough use of mouthwash, putting fingers in mouth).
Stress
Poor diet- eat a balanced diet
Using toothpaste with sodium lauryl sulfate in it. Sodium lauryl sulfate is a cleanser that they put in most toothpastes. There has been studies that suggest that it can act on an irritant to your mouth. People who used toothpaste with out this cleanser have noticed significant reduction in formation. Sensodine(spelling) makes a toothpaste without it although it is expensive.
Health-I have noticed whenever I get a sore throat or feeling run down I get them sometimes.
Acidic foods like citrus, soft drinks, and tomatoe based foods.
What works for me.
Better diet-no fried foods(especially freedom fries), no beef hamburgers, more fruits and vegetables, cut out Coke(soda) almost entirely(one a week as a treat)
,
keeping fingers out of mouth as much as possible( I still chew on skin from time to time, but I'm slowing stopping)
I have my finances in order (reduces stress level).
Use Listerine mouthwash at least 2 times a day and leave it in mouth for over a minute forcing through teeth back and forth.
I don't always use the toothpaste without sodium lauryl sulfate but it does help me.
I have noticed I can go sometimes 3-4 months without a canker sore and I rarely get more than one. I used to have almost at least one at any given time.
Taxman don't use the Hydrogen Peroxide( I know its not 100% I was a chemistry major in college) full strength because it will eat at your enamel on your teeth.