Summary

  • Cold sores are blisters around the mouth and nose, caused by the herpes simplex virus.
  • Cold sores can easily be spread to others, although most adults are already infected. They can be spread even when blisters are not present.
  • Cold sores will get better by themselves except in cases where they get infected by bacteria, occur in the eye or become widespread in people whose immune system is suppressed.
     
Cold sores (herpes labialis) are small blisters that usually form on the lips or skin around the mouth, nose and on the chin. They are caused by infection with the herpes simplex virus (HSV). People are usually infected in childhood or young adulthood, and the infection persists for life. 

HSV infection is very common

Around 90 per cent of adults have herpes simplex antibodies in their bloodstream, which means that they have been infected with the virus at some time. However, the first (or primary) infection does not usually cause any symptoms. One-third of infected people experience cold sores, which are a recurrence of the earlier infection and do not indicate recent infection. Most of these people would not have experienced symptoms from the first infection. 

Symptoms of a primary HSV infection

For some people (mainly children) infected with HSV, the first (primary) infection can cause symptoms. These can include:

  • fever
  • tiredness
  • blisters (lesions) and ulcers in and around the mouth
  • swelling 
  • pain inside the mouth and on the gums
  • a sore throat
  • swollen neck glands. 

The symptoms can last up to 14 days and may cause dehydration, especially in young children, because it is painful to swallow. Primary infections are more likely to be severe in newborn babies, people with atopic dermatitis (often called eczema) and in people whose immune system is suppressed.

Triggers for cold sores

In some people the HSV infection causes cold sores, which erupt following a trigger event such as a cold. This explains the term ‘cold sore’. Other triggers that may cause an attack of cold sores include:

  • feverish illnesses, like influenza, or chest infections
  • sunlight
  • exposure to windy conditions
  • hormonal changes, such as the menstrual period
  • emotional or physical stress.

It is important to remember that cold sores are a symptom of ongoing infection rather than a new infection. The sores usually recur in the same place. 

Cold sore symptoms

Cold sores usually develop as follows:

  • Most people experience localised itching and tingling a day or two before the cold sore appears.
  • A collection of small blisters forms.
  • These blisters can be accompanied by pain, tenderness and a sensation of heat and burning.
  • The blisters burst after a few days.
  • The site develops a crust.
  • The crust dries up and eventually falls off after about 10 days.

 

Cold sore complications

Cold sores are an annoying problem for most people who get them, but they get better without any specific treatment. However, in people with some types of immunosuppression (such as people undergoing chemotherapy, or taking very high doses of corticosteroids such as prednisolone), the cold sores can spread more widely and the symptoms can be more severe. Medication may be required in these cases.

Uncommon complications that require medical attention include:

  • bacterial infections – possible symptoms include redness around the blisters, pus in the blisters and fever
  • cold sores that spread to the eyes, fingers or other parts of the body – a cold sore in the eye causes a painful red eye. Immediate medical attention should be sought, as the herpes virus causes an ulcer on the cornea that can damage sight. However, permanent damage can usually be prevented by early treatment, including medication to suppress the virus. There are other more common causes of a painful red eye, which also require medical review.

There is more than one type of herpes infection

There are two types of herpes simplex infection: herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). Cold sores around the mouth (often called ‘oral herpes’) are generally caused by HSV-1. Most cases of genital herpes are caused by HSV-2. 

Cold sores on the mouth can cause genital infection during oral sex for people who do not already carry the cold sore virus. 

There are many other viruses that are also in the herpes virus family, however the infection and symptoms are different. One example is varicella zoster virus (VZV) which causes chickenpox and shingles.

How HSV is transmitted

The herpes simplex virus spreads between people, usually through contact with saliva or direct contact with a blister. The most infectious time is in the first few days when the blister is forming. Sometimes, people can pass the virus to others when they have no symptoms. This is because the virus may be lying dormant in the skin cells of the lips. 

How to avoid transmitting HSV

If you have a cold sore, be sure to wash your hands after touching it and be especially careful to avoid touching your own eyes after touching your cold sore. It is the fluid contained in the blisters that is considered to be the most infectious. While you have a cold sore it is also important to avoid: 

  • sharing toothbrushes
  • sharing drinking glasses or bottles
  • sharing cutlery
  • sharing towels or other personal items 
  • close contact (such as kissing and hugging) with newborn and young babies
  • kissing others
  • close contact with children with burns or eczema
  • close contact with people with suppressed immune systems.

Preventing the transmission of HSV among children

If young children with a cold sore are unable to follow good hygiene practices, it is recommended that they be excluded from childcare or school until the blister stops weeping. It is also recommended that blisters be covered by a dressing, where possible. 

Treatment for cold sores

Cold sores are generally not dangerous and do not cause any permanent damage to the skin. Treatment does not cure the infection and is not necessary for most cases. Avoid picking the scab or breaking blisters as this can cause secondary infection with bacteria, or scarring. 

Creams to treat the symptoms can be soothing, as can ice on the blisters. Simple painkillers may occasionally be required. Povidone-iodine ointments (commonly known as Betadine) can be dabbed onto the cold sores and may reduce symptoms in some people.

Antiviral medications come in many forms, including creams and tablets. Medications such as aciclovir and famciclovir shorten the duration of the cold sore by reducing the ability of the virus to reproduce. Aciclovir cream works best when applied to the blister at the earliest stages of cold sore development, when the area is tingling. However, not everyone experiences warning signs of an impending cold sore. 

Preventing a cold sore outbreak

There is no cure for cold sores. Suggestions to reduce the number of outbreaks include: 

  • Avoid known triggers, if possible.
  • Wear sunblock on your face and lips when outdoors.
  • Pay attention to your general health and stress levels.
  • Avoid getting ill or run down.

Where to get help

  • Your doctor
  • NURSE-ON-CALL. Tel. 1300 60 60 24 – for expert health information and advice (24 hours, 7 days)
  • Your local pharmacist
References
  • School exclusion table, 2009, Infectious Diseases Epidemiology and Surveillance (Blue Book), Department of Health, Victorian Government. 

More information

Mouth and teeth

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This page has been produced in consultation with and approved by: Department of Health and Human Services - RHP&R - Health Protection - Communicable Disease Prevention and Control Unit

Last updated: July 2017

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