Yes lemon balm will work great to penetrate your skin and prevent and kill off the herpes virus which causes the cold sores.
To get rid of cold sores with lip balm oil or prevent cold sores dilute some lip balm oil and apply it directly to the cold sore 3 to 4 times per day.
You can also get rid of a cold sore using apple cider vinegar applied directly to the cold sore 2 to 3 times per day until the cold sore goes away.
Apple Cider Vinegar contains antibacterial properties which can help kill off the herpes virus too and get rid of cold sores.