I've gotten them all my life, usually on the lips, but during a cold, sometimes under the nose. For me they seemed to come on from irritation, if I was sick, or stress, or too much sun.
For years now, I've been able to avoid them. If I feel one coming on, usually an itchy/tingly feeling in the area, I get out my L-Lysine and Vitamin C, works 90% of the time for me. The couple of times it hasn't worked was because I waited too long to take the supplements, but nevertheless, it definitely lessened the severity.
Right now I use 'Country Life' L-Lysine (free form amino acid). It also contains vitamin B-6 to aid in utilization. They are 500mg. capsules.
My method is frequent mega-doses to start, then lessen. As soon as I feel one coming on, I take 2,000mg of L-Lysine with 1,000mg of vitamin C (ascorbic acid). Three hours later, I'll repeat, only using 1500mg of Lysine and 500 or 1,000mg of C. I continue this for the first day every 3-4 hours.
It really does kick it out of your system. The following couple of days, I continue using Lysine and C, but just a couple of times a day.
I try not to put anything on it at all. I've tried Lysine creams, Carmex type products and vaseline. The moisture just makes them seem to 'fester' and tend to spread.
PS: Once you're sure it's not appearing and you've avoided it, stop taking the L-Lysine. It's better to take it only for the fever blisters/cold sores...more effective that way.