For years I listened to doctors tell me what canker sores were and were not. Through charting over the years, of everything that crossed my lips and when the sores occurred I have finally figured out what affects me. I can't eat anything with pineapple or the juice of pineaple or very much with with any citrus in it. A lot of the manufactures call a fruit juice one thing and then mix other citrus juices in, so I have to watch everything. If I avoid these things I avoid canker sores. Chart what you eat, and it may take months of doing this.