At the Southern California University of Health Sciences, researchers found that a topical ointment containing the essential amino acid lysine effectively reduced the duration of cold sores. In previous studies, lysine was shown to decrease the risk of cold sore outbreaks as well as the duration of the outbreaks. It is believed that lysine inhibits normal replication of the cold sore virus, shortening the normal life span of the infection.
In this small pilot study, 30 participants (15 male and 15 female) were asked to apply the ointment and monitor symptoms such as itching, tingling, burning, tenderness, prickling, soreness, bump/swelling, small blisters, oozing blisters and crusting. By day three, the ointment completely diminished cold sores in 40% of the participants, and in 87% of participants by the end of the sixth day. A cold sore episode may last anywhere from seven to 10 days — and even up to 21 days — without treatment, so these results represent a significant reduction. In addition, there were no adverse effects reported during this study.
Sources: Altern Med Rev. 2005 Jun;10(2):123-7