Cold sores are caused by the herpes simplex virus damaging millions of cells. The virus enters surface nerve cells and the cells are forced to create new virus particles. The cell is then destroyed and releases the herpes simplex virus. After several cells are destroyed by this, it creates an open ulcer, also called a cold sore or fever blister.

The primary protein in the creation of the herpes simplex virus is arginine, which is an amino acid. This is stored in the cell. This is helps the creation of the herpes simplex virus. Lysine is another amino acid stored in the same area in the cell but does not help the creation of the virus.

Foods with higher arginine than lysine, like nuts, grains, chocolate and some vegetables, can cause the cold sores. If you take in more aginine than lysine during one day, you are a candidate to develop a cold sore. But this does not mean you will definitely develop one.