What causes chicken pox?
It is caused by the varicella zoster virus which spreads by direct contact with chicken pox blisters and through droplets breathed out through the mouth and nose.
Generally chicken pox can only be caught once, although there are rare reports of a person having it more often. In some cases, the virus can reactivate following chicken pox causing shingles, which is usually a small area of blisters on the skin.
Who is at risk of developing chicken pox?
The majority of children catch chicken pox at some time. As it is infectious from about two days before the rash appears, children often go to nursery or school when they have it and outbreaks are not uncommon.
It is infectious until all the blisters have formed scabs (usually about seven days). People sometimes think that the scabs have to fall off before the risk of infection has gone, but this is not the case.
The spots, and then blisters, can develop in several phases, so check the child all over to make sure that scabs have formed on all the blisters before sending him or her back to nursery or school.
Chicken pox has an incubation period of eight to 21 days, which means that a child can develop it between eight and 21 days after coming into contact with someone with chicken pox. However, in most cases there is no need to keep the child away from nursery or school if they have been in contact with chicken pox but not caught the illness.
What are the signs and symptoms of chicken pox?
Before the rash appears, a child may seem unwell and have a temperature. The rash tends to start as small red spots which then develop into blisters. It usually starts on the body and face and often spreads to the arms, legs and scalp. It may also appear inside the mouth and nose, and sometimes on the genitals.
After a few days, the blisters start to scab over, but new blisters may still continue to appear. The number of spots varies from person to person. Some children only get a few, while others seem to be covered in them.
How is chicken pox normally diagnosed?
A GP will be able to diagnose chicken pox easily once the rash has appeared as it has a distinctive appearance. The spots are round and form a blister with fluid inside.
How is chicken pox treated?
There is no way of reducing the length of time a child has chicken pox, only making the symptoms more bearable. A vaccine against chicken pox is used as part of the normal vaccination programme in the United States, but it is not currently in general use in the UK.
If the child has a temperature, you should try to bring it down with paracetamol. Try to keep the child cool as heat and sweating makes the itching worse.
It is always a good idea to use a separate towel for the child with chicken pox, although if the child has siblings this is unlikely to prevent them from catching it.
Efforts should be made to stop the child scratching the blisters as this will make them sore and open to infection. The blisters are also more likely to leave a scar if the scabs are scratched off.
The scratching can be reduced by cutting the child’s nails short and persuading them to wear cotton gloves. Calamine lotion will help to reduce the itching but it needs to be reapplied regularly. If the itching is so bad that the child has trouble sleeping, a doctor can prescribe an antihistamine.
If the child has blisters inside their mouth, this can make them feel particularly miserable and not feel like eating or drinking. Watch them carefully for any signs of floppiness or dehydration and seek advice from a GP if you are worried. Cold drinks and soft bland foods can help, but avoid giving the child anything too salty or acidic.
Is it dangerous?
For most children, chicken pox is nothing more than a mildly uncomfortable illness which gets better on its own. However, it can be dangerous for people with immune problems who have had no history of previous chicken pox to come into contact with someone who has active chicken pox.
People who have not had chicken pox and are receiving chemotherapy, taking steroids or have weakened immune systems must always seek advice from their GP, hospital consultant or infection control nurse and may have to have a special injection (VZIG) each time they come into contact with chicken pox.
What happens next?
Once a child has had chicken pox, they will be immune from it for the rest of their life. Catching chicken pox more than once is extremely rare. However, it is possible that the disease could return in later life as shingles, when the virus causing chicken pox is re-activated. A person with shingles can pass on chicken pox to other people who have not had it before, but not shingles.
Chicken pox is unlikely to have any lasting effect on a child. The most common after effect is one or two tiny scars if the scabs have been scratched. In very rare circumstances, other conditions can develop after chicken pox, but this is unlikely.
Last reviewed by Great Ormond Street Hospital: July 2012