The cold sore virus is very common and is carried by up to 80% of the population. It is caused by a virus called ‘herpes simplex’ (HSV). Cold sores are highly infectious and capable of spreading to other parts of the body. Once you have been infected, the virus lies dormant in the nerves that supply feeling to the face and mouth. The virus can subsequently be reactivated, and it is the reactivation that presents as cold sores on the lips.


It is important in managing this condition to identify what triggers an outbreak of cold sores. Most cold sore sufferers can identify everyday events that cause the reactivation of the virus and lead to the development of a cold sore. These triggers can vary between individuals, for example, where one person is more affected by the cold, another sufferer may be more susceptible to sunlight. Identifying the trigger is the first step to take towards managing cold sores.

Common trigger factors include:-

  • Ultraviolet (UV) light from sunshine or sun bed exposure.
  • Emotional stress or exhaustion.
  • Common cold, flu or feverish illness.
  • Feeling physically low or fatigued leading to a weakened immune system.
  • Menstruation.
  • Exposure to extreme temperatures or weather conditions.
  • Pregnancy.
  • An injury to the mouth, surgical operation or dental treatment.
  • A knock on the lips or face.

The cold sore cycle

There are five different stages:


This stage normally lasts between a few hours and a day. The cold sore is ‘invisible’ at this stage but a tingling or burning sensation may be felt. If an antiviral cream (aciclovir) is applied at this stage it may prevent the visible signs of the cold sore from appearing. Aciclovir attacks the virus and stops it from multiplying.


This stage is characterised by a small group of painful, fluid-filled blisters. These are normally seen on the second day of the cold sore cycle. Here again, treatment with an antiviral cream will reduce the life of the cold sore.


Once the small blisters have burst, a weeping ulcer is seen that may last for several days. This stage is also very painful. The clear liquid that is released from the ulcer contains a high number of viral particles and as such is highly contagious.


After about 4 days a thin scab will form, acting as a protective covering for the new skin that is forming beneath. The skin around the scab may dry and crack and even bleed. Moisturising the area will help to reduce this. The scab may also be itchy, but is not contagious at this stage.


After 9 – 12 days the cold sore will have healed. A slightly red/pink area of skin will remain but will quickly fade. Most people who get cold sores will usually experience around 2 – 3 attacks per year although some people may get as many as 12.

Reduce the risk of spreading the virus

  • Try not to break the blisters or pick the scabs.
  • Always wash hands after touching the cold sore or applying medication.
  • Avoid kissing.
  • Do not touch the eyes and take extra care when applying or removing make-up.
  • Do not wet contact lenses with saliva while suffering a cold sore and always wash the hands before touching your lenses.
  • Sharing eating or drinking utensils, such as cutlery and cups, should be avoided, especially with children.
  • Avoid oral sex if a cold sore is present since this may lead to genital herpes.
  • Do not share personal hygiene items such as toothbrushes, face cloths or towels.
  • Make sure the cold sore is healed before visiting a dentist.
  • NB. Consult a doctor if a cold sore becomes severe or extensive.

Once infected, the virus cannot be removed. There are medicines available to treat the first episode of infection and to treat recurring cold sores. These are a few key points to remember when treating cold sores:

Treat the cold sore as soon as it starts developing (the tingle stage) as this can reduce the duration of the cold sore by up to 50%.

It is never too late to start treating a cold sore as even during the blister stage, antiviral creams are effective.

An untreated cold sore will usually last between nine and eleven days.

Treatment with an antiviral cream will also help prevent the spread of the virus.

Treating the first infection

For an adult or child over two years old with a first infection, tablets from your dentist or doctor can be taken five times a day for five days.

Treating recurring cold sores

To treat recurring cold sores, antiviral cream can be applied five times a day for five days beginning as soon as the tingling sensation begins, or as soon as the cold sore appears on the lip. The cream can be bought from a pharmacy, but the tablets must be prescribed by a dentist or a doctor.

For further help and advice regarding cold sores, please telephone the Cold Sore Information Bureau (CSIB) 0845 603 0052 or visit their website .