Causes
Cold sores are actually caused by the herpes simplex virus (HSV) which attacks the skin and nervous system. They are the most common manifestation of a herpes simplex virus infection (herpes simplex virus one (HSV-1) or herpes simplex virus two (HSV-2) and are very contagious and cannot be cured.
Generally it is felt that anything that compromises the immune system may trigger cold sores, such as infection, cancer or any illness. Some women may find that they get cold sores during or just before menstruation and strong, direct sunlight may trigger cold sores in some people. Individuals with weakened immune systems though, tend to get more cold sores and heal slower.

