★★★★★
Many years ago in China, a local doctor gave me a vial of Bingpengsan (borneolum and borax), which is a white or pink powder. She told me to rinse my mouth three times a day with diluted hydrogen peroxide (4 parts water, 1 part hydrogen peroxide). After rinsing, I was to use the equivalent of a Q-tip to spread the Bingpengsan lightly on the cold sore. This must be done immediately when the cold sore just emerges.
Within a day the cold sore will dry up, but keep using the treatment. About day three, the cold sore will have turned into a scab and will fall off. I've kept the vial for more than 25 years and use it whenever I feel/see a cold sore emerge. It has never failed to eliminate the cold sore immediately. I'm not sure where or how to get this type of powder in the U.S., but my acupuncture doctor has provided to me a powdered preparation in capsules called Tianqi, which has the same effect on open wounds (like blisters, burns, scrapes, bed sores). Just take the the powder out of the capsule and sprinkle or spread it on the open sore (if it's a blister, just put the powder on it). The wound will dry up and scab over very, very quickly. I've never tried the Tianqi for cold sores, but it seems to have the same action as the Bingpengsan.