I dab my coldsore with perfume at the first initial tingling blister stage, and continue to dab it numerous times throughout the day, pretty much every hour.
In most cases this treatment stops the development of the coldsore. At the moment I am in day 2 of the blister stage and can't see anything on my lip. This treatment stings a little but is effective. Most of the time the coldsore doesn't eventuate. If you don't get to it in time and the coldsore does develop, still dab it with perfume numerous times a day. This will reduce the size of the coldsore and lessen the duration of the outbreak.