The herpes simplex virus that causes a cold sore can lie dormant in the body for months or years at a time, causing no symptoms. It is thought that, when a cold sore does occur, it is due to one of a number of possible triggers, including illness such as a cold or flu, feeling stressed, exhausted or “run down”, exposure to strong, direct sunlight, & menstruation, conditions causing immunosuppression (such as AIDS or a course of chemotherapy).
A cold sore is a small, fluid-filled blister that grows on or around the mouth, turning into a weepy sore that can be painful & uncomfortable. It is caused by the herpes simplex (HSV-1) virus which, once contracted, lives dormant in the body for life, causing occasional outbreaks. They are common, affecting around 1 in 5 people in the UK.
The first sign that a cold sore (sometimes also called a fever blister) is on its way is a tingling or itching sensation on or near the lips or nose, accompanied by an area of redness or irritation on the skin. This tingling sensation may continue for up to a day, before the blister appears. The cold sore may begin as one single blister or a cluster of tiny blisters, which are filled with fluid & usually painful. These blisters may last for some days, possibly weeping fluid or bleeding. Eventually they break & begin to crust & scab over, at which point they can be extremely painful & uncomfortable, taking many days to heal.
Cold sores are highly contagious, especially in their initial blister stages, & at this time it is advised that you avoid kissing anyone or allowing any skin contact with the sore. It is also a good idea to avoid touching or picking the sore, & washing your hands afterwards if you do.
Although the diseases are very similar, cold sores are caused by the HSV-1 virus, which is different to the virus that causes genital herpes (HSV-2). HSV-1 sores appear usually on the face, around the mouth, whereas HSV-2 sores appear below the waist, usually on the genitals or rectum.
The virus lives in the nerves, & it is possible to have the virus without showing any symptoms. For some people who have HSV-1, they may barely ever get an outbreak of an actual cold sore. For others, outbreaks can happen as often as once a month.
Although cold sores can appear on the cheek or nose, they are most commonly found on the lips & around the mouth. It is typical that a person with recurrent cold sores will always have them in the same spot.
A cold sore is not the same as a mouth ulcer or canker sore.