Cold sores

Reviewed by Dr John Pillinger, GP

What are cold sores?

Cold sores are a very common illness caused by the herpes simplex virus (HSV).

The disorder is characterised by groups of fluid-filled blisters which appear on red swollen areas of the skin or on the mucous membranes. The areas can be tender and painful. The blisters heal without scarring but have a tendency to recur.

There are two types of herpes simplex virus.

HSV-1, which is the most common type, usually causes cold sores (oral herpes). HSV-2 usually causes genital herpes. But both types can infect any area of the skin or mucous membranes.

Approximately 80 per cent of the adult population have antibodies against HSV-1 in their blood.

Around 25 per cent of the adult population have antibodies against HSV-2.

What causes the virus?

The virus can only be transmitted by close personal contact such as kissing. Most people will have come into contact with the virus between the ages of three and five but will not show any symptoms until after puberty.

HSV invades the cells of the epidermis, the outer layer of the skin, causing fluid-filled blisters to appear. The virus travels from the epidermis along the nerve paths to the roots of the nerves where it becomes inactive.

A weakening of the body's defences, due to a severe cold for example, can lead to a reactivation of the virus and a return of the blisters.

What are the symptoms?

The primary infection can progress in different ways. Some people only have very mild symptoms or none at all. The first outbreak starts one to three weeks after the virus has been contracted. It subsides spontaneously within a few weeks. Later, if HSV is reactivated, the blisters will return.

The first symptom of an outbreak is an unpleasant tingling feeling in the skin. After a short while, a number of fluid-filled blisters appear.

The sores become covered by scabs that, typically, fall off after 8 to 10 days. The virus can spread until the sores are completely covered by scabs.

Around 20 per cent of the people with HSV antibodies have recurrent attacks of cold sores throughout their lives.

In children, the virus can infect the mouth and throat. The infection may be accompanied by a fever and general aches and pains.

What can be done to prevent cold sores?

Avoid direct contact with the sores. These can appear on every part of the body, including the fingers and genitals.

Wash your hands after touching the lips.

Avoid picking at the sores as this can spread the virus to other parts of the body or result in a bacterial infection of the sores.

The body's defences can be strengthened by a healthy lifestyle. Eat a varied diet, exercise regularly and get enough sleep.

The factors which trigger outbreaks differ from person to person.

Menstruation, fever and exposure to sunlight can cause a reactivation in some people. In others, there is no demonstrable cause. Using a sunblock may help to prevent a reactivation.

How are cold sores diagnosed?

A combination of the patient's medical history and the appearance of the sores will usually be sufficient for a diagnosis. A scrape or a blood sample can be used to confirm it.

Possible complications

The sores may become infected by bacteria.

If the condition spreads to the eyes, it can damage vision.

In patients who suffer from atopic dermatitis, the cold sores can, in rare cases, spread to larger parts of the body.

Massive cold sores can be a sign that another disease, pneumonia or HIV for example, has weakened the body's defences.

How are cold sores treated?

Treatment is aciclovir 5 per cent cream (eg Zovirax cold sore cream), applied to the cold sore five times a day for five days. This can be bought over-the-counter from a pharmacy or obtained on prescription.

The treatment should be started as soon as the first symptoms appear. It can often reduce the length of the outbreak and the infectious period.

Recurrent severe attacks can be treated by anti-HSV agents in pill form.

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