Cold Sores

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How do cold sores occur?

Cold sores are caused by the herpes simplex virus. A first cold sore usually occurs in childhood. The virus infects through the moist 'inner' skin that lines the mouth. It is commonly passed on by skin contact such as kisses from a family member who has a cold sore.

After the first infection, the virus settles in a nearby nerve sheath and remains there for the rest of your life. For most of the time, the virus lies dormant (inactive) and causes no symptoms. However, in some people the virus becomes 'active' from time to time. When activated, the virus multiplies and travels down the nerve sheath to cause cold sore blisters around the mouth. Some people have cold sores often, others only now and then. It is not clear what causes the dormant virus to become active. Some things that may 'trigger' the virus to activate and cause a cold sore include:

• Illness. Cold sores may occur during feverish illnesses such as colds, coughs, and 'flu.
• Menstruation. Cold sores are common around the time of monthly periods.
• Stress or just being 'run down' for one of many reasons.
• Sunshine. Strong, direct sunlight may trigger cold sores in some people.

What are the symptoms of cold sores?

You may feel a tingle or itch before the blisters appear, usually around your lips or nose. This can last several hours, or up to a day or so. After the tingle, one or more blisters appear which are usually sore. They may weep and take several days to scab. The scab slowly disappears over a week or so leaving no scar. Some virus will remain dormant in the nerve sheath ready to cause another cold sore sometime in the future.

Can cold sores be passed on to other people?

Yes. When you have a cold sore you should not kiss anyone or allow anyone to come into skin contact with the sore. In particular, avoid kissing newborn babies and anyone who has a poor immune system such as people on chemotherapy or with AIDS. However, when you have no symptoms (when the virus is dormant), you are not usually infectious. Also, healthy people who already have cold sores cannot be re-infected.

What are the treatments for cold sores?

• If you find that sunlight triggers your cold sores try using sunscreen lip balm when out in bright sunlight. This has been found to prevent some bouts of cold sores in some people.
• Pain can be eased by painkillers such as paracetamol or ibuprofen.
• A pharmacist can advise a soothing cream or gel.
• Antiviral creams. You can buy these at pharmacies or get them on prescription. These do not kill the virus, but prevent the virus from multiplying. They have little effect on existing blisters, but may prevent them from getting worse. So, if you use an antiviral cream as soon as symptoms start then the cold sore may not last as long, and may be less severe. There is debate as to how well these creams work. Some people say that they help a lot to limit symptoms. Others feel they make little difference.

© EMIS and PIP 2006   Updated: June 2006   PRODIGY Validated

The authors and editors of this article are employed to create accurate and up to date content reflecting reliable research evidence, guidance and best clinical practice. They are free from any commercial conflicts of interest. Find out more about updating.

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