Cold sores (also known as fever blisters) are a result of certain
strains of the herpes virus. Herpes can be contracted from another
person who has an active lesion. Shared utensils, razors and towels can
all pass along the herpes virus. Once a lesion has occurred, the virus
can lie dormant in nerve cells and can emerge again.
Itching or a heightened sensitivity is commonly experienced at the
site before a lesion erupts. Fever, stress, exposure to the sun and
menstruation may trigger a recurrence.