As you probably know, fever blisters are a form of herpes that lies dormant in the nerve root and can be triggered by various different factors. I also hadn't had a fiver blister in a few years and then suddenly got one again. Some of the things that seem to trigger mine are extreme stress, illness, wind burn, and sun burn. Some people say taking Lysine daily will help, it didn't seem to make any difference to me. I put Campho Phenique on mine the second I feel a blister coming on and put it on several times a day as long as it's there and that seems to keep them from getting very big and they don't last nearly as long. You can also get a prescription for an anti-viral that you take at first signs of a fever blister, but the medication is usually over $100 per course so I never chose to go this route. Good Luck!