I used to get canker sores all the time, now I seldom get them. There is a medicine called Negatan (45%)that I had filled by prescription (from the dentist)that works wonders. It is a red dye - comes in a bottle with a dropper. You only need to put one drop on each canker sore and within a day or two they are gone. The medicine is very strong! It burns when put on the canker sore, but it really works. I had this medicine filled in Mechanicsville, Virginia when I lived there. I currently live in Maryland and cannot get the prescription filled here.