Cold sores Dr Trisha Macnair Cold sores may be unsightly, but they're common among young children. We look at the causes and the best ways to prevent recurrent outbreaks.

In this article

What are they? What causes them?

Who's affected? What are the symptoms?

What's the treatment? Further help

Cold sores are recurrent blistering spots that appear around the mouth and nose.

The virus is picked up through contact with someone who has active infection

Cold sores are caused by an infection with the herpes simplex virus, usually the herpes simplex virus type 1 (HSV-1). The virus is picked up through contact with someone who has active infection (for example, from someone who has a cold sore) - the virus is passed on in saliva.

After an incubation period of three to five days, the initial infection (sometimes called the primary infection) may cause a variety of problems, although in the majority of cases there are no symptoms and it goes unnoticed. The virus isn't cleared from the body but lies dormant (inactive) deep in the nerve cells.

Certain triggers can reactivate the virus, causing it to travel down the nerve to the skin surface where it produces a cold sore. Triggers include illness, stress, UV light (exposure to bright sunshine) and cold.

Cold sores are common, but outbreaks often become less frequent as a child gets older. Most adults have antibodies to the cold sore virus, suggesting that during childhood we all come into contact with the virus and some of us develop immunity, while others get the sores.

The primary infection may be symptomless, but can cause illness, especially gingivostomatitis (acute inflammation of the mouth and gums) with high fever and extensive ulcerating lesions on the lips, tongue, gums and palate.

There may be an initial tingling sensation

Recurrent infection causes cold sores, which may be single or multiple. There may be an initial tingling sensation in the skin several hours before blisters appear, which sufferers can learn to recognise as a warning. Small inflamed spots then appear, which may be itchy, sore or irritating. The spots turn into blisters that crust over after a couple of days and slowly heal in about ten days.

Cold sores have a typical appearance, usually occurring on the margin of the lip where the red mucosa meets skin. A doctor can confirm the diagnosis.

Treatment includes learning to recognise and avoid triggers (for example, by applying sunblock or herbal cream to the lips when going out in strong sun). Antiviral cream (aciclovir) can be bought at the pharmacy and helps shorten the duration and intensity of the sores. This must be applied to the skin as soon as possible for best effect, ideally as soon as the tingling is felt.

There's a small risk of more severe sores, especially in children who are immunocompromised or who have skin problems such as eczema. Encourage your child not to touch or pick their sores and to wash their hands regularly to reduce the risk of spreading the infection.

This article was last medically reviewed by Dr Rob Hicks in January 2008