Natural Factors L-Lysine - 1000 mg - Provides relief from the herpes simplex virus (HSV), helping reduce the recurrence, severity, and healing time of cold sores. As one of the nine essential amino acids that the body relies on to manufacture protein, L-lysine has important roles in the synthesis of collagen, tissue repair, and the production of hormones and enzymes. This makes L-lysine an important nutrient for maintaining a healthy immune system, especially when combined with an adequate intake of vitamin C.