Cold sores are a form of the herpes simplex virus known as HSV I. Cold sores are generally small, painful, fluid-filled blisters on the mouth or nose. Infections caused by this virus are contagious and can be spread from person to person through close contact with a lesion or even normal skin shedding the virus. It is primarily passed on through kissing. The virus is most contagious when the blisters are active. The chances of catching herpes (cold sores) from surfaces and towels are close to impossible. When cold sore lesions appear in their most common location, around the mouth and lips, people often refer to them as "cold sores" and "fever blisters."

Some of the more significant symptoms that appear before an outbreak include tingling, itching, and burning in the mouth or nose area. This is known as the prodromal stage, meaning symptoms that indicate an outbreak is imminent. Following this stage within hours to a few days, the infected area becomes red and fluid-filled blisters start to develop. The blister may than cluster to form one large blister. Other symptoms include mouth soreness, sore throat, fever, or swelling of the lymph glands. Once the blisters are developed, they usually break open, leak the fluid, and crust over and disappear. This usually takes several days to a week.  Once the blisters disappear the virus goes into a dormant stage in the nerve cells until it is time to replicate again for another outbreak.

Recurrences of cold sores are more likely if you are suffering from a fever, cold or flu, are exposed to ultraviolet radiation, are under stress, have changes in your immune system, or trauma to the skin. Many times there are no apparent causes for an occurrence. Cold sores are not curable, but with medication or supplements, you can lower the chances of an outbreak.

Occasionally this virus may cause blisters on the fingers. If the virus gets into the eye, it can cause conjunctivitis (swelling of the inner surface of the eyelids, sometimes called "pink-eye") or even a corneal ulcer (open sore on the cornea). On rare occasions, it can spread to the brain and cause the brain disease encephalitis.