While I don't have a cure for cold sores, I discovered what causes a breakout on my upper lip. I recently found out that I have a cousin in another country that has a break when she eats too many tomatoes. So I decided to keep track of what I ate, when I have my breakouts. It turns out that citric acid was the culprit. I noticed that when I drink too much orange juice, cranberry juice, soda, or eat tomato sauce, I get a cold sore. Any one item does not cause me to break out, but ingesting multiple items in one day or over a few days will result in a painful breakout that lasts about three weeks. Now, I very seldom get a cold sore, and when I do, I realize that I was not careful about what I ate, especially when it is often used as an additive is foods, like most sodas, jellies, sour dough bread, etc. I thought I would pass this information on, in case it helps someone else prevent or reduce future cold sore break outs, as they are painful and embarrassing.