The reason I am writing this is because I have looked through many remedies and not seen this one yet! One thing I discovered that works better for cold sores than anything I have ever tried is to use Bactine!
Whenever I notice that I'm getting a cold sore, I take a Q-tip and dip it in Bactine and rub it on the sore very vigorously. I do this for about five minutes, making sure the Q-tip stays soaked. I rub the sore until it breaks open and then stop completely.
Obviously, the earlier you catch it, the better.
The Bactine numbs your lip and any other part of your body that it touches. It will kill any infection in the sore. After a couple hours, you will notice that the sore isn't growing anymore, and will only heal from here on out! It has worked every single time I have tried, without fail. If nothing else, it gets you passed the nasty looking stage of the sore!