Cold sores

What is a cold sore?
A cold sore is a small, painful, raised area of small, fluid-filled blisters. They usually happen where the lip joins the surrounding skin. The blisters are painful and dry up to make a yellow crust which gradually heals in a few days.
Cold sores are usually found on the lips but you can get them in other places, such as in the nostrils, on the nose or around the outside of the mouth. Cold sores tend to last 5 to 7 days and can keep coming back. Most people only have them once or twice a year.
How do I get cold sores?
Cold sores are caused by a virus (a 'Herpes Simplex' virus). You first get this virus in childhood or early adulthood, and it may cause a fever and mouth ulcers (called 'primary herpetic gingivostomatitis').
About a third of people who get this 'primary' infection go on to develop cold sores in later life. However, many people with cold sores did not get this primary infection.
What brings on the cold sores?

Cold sores usually appear when...