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Cold sore
A cold sore is a blister that appears on or around the lips or the mouth. It is caused by a viral infection and is highly contagious. Around 1 in 5 people in the UK have cold sores that recur frequently.
Cold sores are caused by a virus called the herpes simplex virus (HSV). There are two types of herpes simplex virus - HSV-1 is the type usually responsible for cold sores, while HSV-2 usually causes genital herpes. Both types can infect any area of the skin, but having one type does not mean a person will get the other.

The viral infection is highly contagious and is easily passed from one person to another through physical contact with someone who gets cold sores, for example through kissing, or from people who do not get cold sores but who carry the virus in their skin. Such people often do not even know they are carriers.

The virus can be caught by physical contact during early childhood but symptoms do not usually appear until the teens or early adulthood. Once a person has caught the virus, that person also becomes a carrier. The virus stays dormant most of the time, living in the nerve endings in the skin. It is only when the virus is activated by a trigger, for example an emotional upset, a menstrual period, exams, sunlight or temperature change that it starts to multiply and move down the nerve endings to the skin surface where it forms a blister.
When cold sores appear it means the virus has been triggered to move from its dormant to its active phase. Cold sores appear as single blisters or clusters of blisters and they last about ten days. The blisters are painful, tender and red, and are filled with pus-like fluid. During the time the cold sore is visible, the blisters will burst, weep a clear fluid and eventually form a scab. Cold sores can get worse if a bacterial infection sets in to the broken skin layer.

The first time a person catches HSV-1 they will show only mild symptoms or no symptoms at all. However, once a person has the cold sore virus, they are likely to have recurring cold sores at the same site for years to come. Because cold sores recur it is possible to learn to recognise when a cold sore is about to appear as it causes a tingling, burning or itching sensation around the mouth and lips.
Simple over-the-counter treatments such as creams containing the antiviral agents aciclovir or penciclovir can be used to treat cold sores. These need to be used as early as possible, preferably during the tingling stage, to stop the blister from appearing. Early use of these treatments may not actually stop the cold sore appearing, but they can shorten the duration of the attack even if applied at the blister stage. Other treatments can help soothe, numb or dry up the blister.
When to see your pharmacist
Your pharmacist will be able to provide you with antiviral creams containing aciclovir or penciclovir to treat your cold sores without the need for a prescription. The creams should be applied at the first signs of the cold sore developing.

If you know that your cold sore is triggered by sunlight or strong winds, before you take your summer or winter holidays, talk to your pharmacist about the use of lip balms containing sun blocks that will help reduce the chances of the cold sore appearing.

If your cold sore is particularly painful, your pharmacist will be able to recommend analgesics to provide pain relief.
When to see your doctor
See your doctor if the cold sore lasts longer than two weeks and has not improved with over-the-counter treatment. If your eyes become sore, see your doctor as soon as possible as it may mean that you have transferred the cold sore virus to your eyes. Viral eye infections need immediate attention to avoid damage to your sight. If your cold sore is particularly severe or occurs very frequently, your doctor may prescribe tablets containing aciclovir or valaciclovir.
Living with cold sores
Cold sores are not life threatening and usually go away by themselves within two weeks without leaving scars. However, they are unsightly and it is natural to want to get rid of them as quickly as possible, or even stop them appearing in the first place.

The first thing you can do is to try and avoid the triggers that bring on your cold sores. If you know that your cold sore is triggered by sunlight or strong winds, apply lip balms containing sun blocks when outdoors during your summer or winter holidays. Wear a hat in the summer to protect your face from the sun, while in the winter cover your face with a scarf to protect against the wind.

Learn to associate the tingling sensation with the appearance of the cold sore, and take immediate action. Applying an antiviral cream at the first signs will help reduce the cold sore and may even prevent it all together. If your cold sore occurs repeatedly, it is worth keeping a supply of antiviral cream in the house so that it can be applied without delay.

If you do get a cold sore, do not scratch or pick it. You risk causing a skin infection and you can transfer the virus from the cold sore to your eyes through touch. Be particularly careful if handling contact lenses if you have a cold sore. Be sure you wash your hands thoroughly to avoid transferring the virus to your eyes when you insert your contact lenses.
Useful Tips
  • Find out what normally triggers your cold sores and try and avoid them - for example, staying out of sunlight or trying to avoid stress
  • Avoid touching your cold sore or coming into contact with other people's cold sores
  • Wash your hands regularly when you have a cold sore to stop spreading the virus
  • Don't touch your eyes when you have a cold sore in case you spread the virus to the eyes which may result in infection
  • Stay healthy by eating well and taking regular exercise - feeling run down means your body defences are down and this can trigger an attack
  • Try and treat the cold sore as soon as you feel it starting

Reviewed on 14 November 2010