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Cold sores

Herpes; virus; cold; sore; stomatitis; mouth; blister; skin; simplex; sores; fever; ulcer ;

Cold sores are caused by a virus called herpes simplex virus (HSV). Cold sores are very common. About 20% of children will have been infected by the age of 5 years and about 80% of people will have been infected by the time they are adults. 

After the first infection, the virus that causes cold sores 'hides' in the nerves of the skin (usually around the lips), and can cause new cold sores from time to time.


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What is herpes?

  • There are two main types of herpes simplex virus (HSV). HSV type 1 viruses mostly cause sores around the mouth, but they can also cause lesions inside the mouth and on other parts of the skin. The other type are HSV type 2 viruses which cause most genital herpes. (See 'Genital herpes' on the Department of Health South Australia website).
  • The virus that causes chicken pox and shingles is also a herpes virus (herpes zoster virus), but cold sores cannot cause chicken pox or shingles, and chicken pox does not cause cold sores. 

How long do they take to develop?

Cold sores take from 2 to 12 days, average 6 days, after contact to develop.

Signs and symptoms of cold sores

  • The first infection with herpes simplex virus is usually so mild that you may not know a person has been infected. The person may not develop any sores.
  • However sometimes the first infection can be severe with large numbers of sores in the mouth (see 'Cold sores in the mouth' below), or sores on top of other rashes (eg on eczema or nappy rash). A person may be very unwell for several days, with a high temperature and pain.

When most cold sores come it is because the virus which is in the skin becomes active again, usually in the same place as they have had cold sores were before.

  • The most common place for cold sores is on or next to the lips, less often on the nose, chin and other parts of the face. But they can come on any part of the body. In babies, they quite  often come on the chin of a dribbling baby.
  • There is often a irritation or burning feeling first, then two or three blisters form, which break, form a yellow scab and then heal. They usually don't leave any scars. Cold sores usually last from 3 to 7 days.
  • Some people have a lot of pain with cold sores and young people may be very embarrassed when they have them, because of how they look.
  • Cold sores can be triggered by things such as cold, sunburn, menstruation (periods), fever, illness, or worries and stress.
  • Some people get one or two cold sores, and never get them again, others get them several times, while for some people they come back many times. The reason for this is not known.
  • The virus can (rarely) affect the eye. Cold sores on the surface of the eye can affect eyesight and any person with a painful red eye should be seen by a doctor.
  • The sores can become infected by other germs as well.
  • People who have immune system problems (such as people who are being treated for cancer) can have a severe illness, which can include encephalitis (infection of the brain).

Treatment of cold sores

  • Using antiviral creams or lotions such as idoxuridine or aciclovir (eg Zovirax**, Betadine Cold Sore cream**) at the very early stages may help keep the sore small and help it heal more quickly.
  • When the first signs of a sore come, (the itching or tingling), it may help to hold an ice cube on the area for about 5 minutes every half hour, for a couple of hours. Some people find that when they do this a sore does not develop, or that it is smaller and does not last so long.
  • It is important to try to stop any other germs getting into the cold sores so try not to scratch them, and be careful with cleanliness. If the cold sore does become infected, antibiotics from a doctor may be needed.
  • Putting alcohol on cold sores appears to slow down healing, and is painful.
  • Gentian violet should not be used, especially on children, because it is poisonous.
  • Some people think that Vitamin E (oily form) may speed up the healing.

**Any products referred to in our health topics are usually well-known brands readily available in Australia. The brand names are given as examples only, and do not necessarily represent the best products, nor the full range of effective products on the market.

Cold sores in the mouth (stomatitis)

  • The first infection with cold can cause a lot of very painful sores in the mouth. This mostly happens in young children (aged 1 to 3 years) but can happen in older children and adults.
  • Usually the symptoms start abruptly with pain in the mouth, the child refuses to eat, dribbles, may have a high temperature and bad breath.
  • The blisters are hardly ever seen because they burst quickly.
  • The sore that is left is from 2 to 10 mm in diameter, covered with a yellow-grey skin. This comes off and leaves an ulcer.
  • This usually happens inside the cheeks and on the tongue but they can come anywhere inside the mouth and throat.
  • They heal within 4 to 9 days, and the pain stops about 2 days before they are healed.

Note: these ulcers are not the same as the common ulcers in the mouth. Ordinary mouth ulcers are usually single and may come back but are not caused by herpes virus.

Managing cold sores in the mouth

  • It is important to recognise that they cause a lot of pain, and that while it is not important for a child to eat while he is ill, having drinks is essential.
  • The child may be willing to have cold drinks or soft foods such as ice-cream, ice-slush, jelly etc.
  • If the child is not able to drink anything, or is very distressed, he may need hospital treatment.
  • Mouth washes with chlorhexidine and lignocaine can help with mouth hygiene and comfort. Ask your chemist about these.
  • Paracetamol or ibuprofen can help with the pain.

Preventing cold sores.

  • Since cold sores are often triggered by sunburn, make sure the child wears a hat and sunscreen.
  • If the cold sores are coming back very often, some preventive medicine may be prescribed by a doctor, but this is not usually done.

Protecting others

  • People with cold sores should not have close contact with newborn babies, people with widespread eczema or burns, or people who have problems with their immune system.
  • The virus is most likely to spread in the saliva of a person has a cold sore that has not yet healed, but some virus can still be in saliva when there is no sore, and the infection can still be passed to another person.
  • There does not appear to be a link between contact with someone with a cold sore, and re-starting of the virus in the other person.
  • The South Australian Department of Health does not recommend keeping a child away from others (eg school, child care) unless the person with the cold sore is in contact with young babies.
  • Cold sore virus is present in saliva (spit), so your child might be protected from catching the herpes virus, if she has not already been infected, by avoiding kissing someone with an unhealed cold sore, or sharing food, cups, etc.
  • Used tissues or other material that has touched the cold sore or saliva should be put in a bin where other children cannot touch them.
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The information on this site should not be used as an alternative to professional care. If you have a particular problem, see a doctor, or ring the Parent Helpline on 1300 364 100 (local call cost from anywhere in South Australia).

This topic may use 'he' and 'she' in turn - please change to suit your child's sex.

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