while its not a proven scientific fact, the amino acid, L-Lysine, will prevent your fever blisters. My husband suffered since he was a small boy, not with just one, but many at a time. And it seemed he always had them. I read about Lysine and we tried it, a couple a day and if he still broke out , we increased the amt. until he no longer broke out. he continued to take them and when he would stop, they would come back. Now he only takes them when he has an outbreak, it makes the pain and symptoms lesser, and also clears it up quicker. It works, try it.it is a natural product of our body, some people are just deficient in it.