Fever

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Key points to remember

  • fever means the temperature of the inside of the body is higher than normal
  • if your child looks unwell and you are worried, take them to a doctor whether they have a fever or not
  • if your child has already seen a doctor but they are getting worse, you should take them back for another check
  • fever actually helps your child’s body fight off infection
  • a fever in a child is usually caused by a viral infection
  • a fever may make your child feel unhappy, but even a high body temperature is very unlikely to cause permanent harm
  • the reading on the thermometer is not the most important clue to how serious the illness is

Young babies (less than three months old) need more cautious treatment.

  • if your baby is unwell or you are worried see a doctor urgently
  • young babies cannot control their body temperatures well
  • a sick baby may feel hot or cold to the touch
  • a thermometer reading is not the most useful way of deciding if your baby is sick

What is fever?

The normal temperature inside your child’s body is around 37 degrees Celsius (but it can be up to 38 degrees). There is a fever when the body temperature is more than 38 degrees Celsius. Fever by itself does not tell you whether your child is seriously sick.

When you measure a child’s temperature, you are trying to tell how hot they are inside the body. This is called the “core temperature”.

The brain helps to control the core temperature and to keep it around the normal level. A young baby (less than three months old) is not as good at controlling their temperature as an older child is.

Fevers are sometimes described as “mild”, or “high”. A mild fever usually means up to 39 degrees Celsius; a high fever usually means more than 39 degrees Celsius.

You can measure a child’s temperature when they feel hot if you want to. But it is not really necessary to do this, especially if your child seems well.

The number on the thermometer cannot tell you:

  • what is causing the fever
  • how sick your child is
See How to take a temperature on this website.
 

What causes fever?

The most common cause of a fever in a child is a viral infection. A bacterial infection is a much less common cause.

The body’s natural reaction to infection with a virus or bacteria is to raise the temperature inside the body (the core temperature). This helps to kill the infection.

Other causes of high body temperature include:

  • immunisations - these usually cause only mild fever
  • wrapping a baby in too many warm layers of clothing, or bedding

Will a fever harm my child?

Fever is a normal way for a child to fight an infection. Being hot may make your child feel unhappy or uncomfortable, but the high temperature is very unlikely to cause any long-term problems.

Some children have convulsions when they have fevers. These may look very worrying, but even these febrile convulsions are very unlikely to cause long-term problems.

See Febrile convulsions on this website.

How do I treat a fever?

Undress your child so that they are just wearing a single layer (for example, a singlet and pants). Make sure the room is not too hot or too cold. These are the best and most comfortable ways to bring your child’s temperature down. Putting your child in the bath or shower to cool them is not recommended.

Your child is their own best guide to the level of activity that you allow. They may need extra rest or they may want to play. Encourage them to drink fluids and eat healthy small meals.

If your child is happy, and they are not unwell, you do not need to do anything more. You do not need to treat the fever with a medicine.

If your child is miserable because of the fever, you can give paracetamol to make them more comfortable. You must follow the dosage instructions on the bottle. It is dangerous to give more than the recommended dose.

Paracetamol may reduce the effectiveness of childhood vaccinations to stimulate lasting immunity (infection-fighting ability). For this reason, it's not recommended for routine use before or after vaccination.
 

How do I know when my child has a fever?

Sometimes you can tell your child has a fever because they feel warm to touch. If your child is happy and does not seem unwell, you do not need to measure the temperature. 
 
If your child is miserable and seems unwell, you can use a thermometer to take their temperature.
 
See How to take a temperature on this website, for detailed instructions.
 

When should I seek help?

Young babies (less than three months old) need a different and more cautious approach. See What is special about young babies?.
 
A fever by itself does not mean your child is seriously sick. Even an ordinary cold can cause a high fever in a child. The important thing is to check for other signs of your child being unwell. 
 
If you are worried about your child, whether or not there is a fever, you should take them to see a doctor.
 
Tell your doctor if your child:
  • has been overseas in the last few weeks
  • has had contact with an infectious disease
  • has been in contact with a sick animal
You should see your doctor if the fever lasts for more than two days.
 
If your child has already seen a doctor but they are getting worse, you should take them back for another check. It can help to take your child back to the same doctor but this won't always be possible.
 

What is special about young babies?

Young babies (less than three months old) need a different and more cautious approach.

  • babies are not very good at controlling their own body temperature
  • babies need to be kept warm - but they can get too hot if they are wrapped in too many layers when they are in a warm place. A good guide is to dress your baby in one more layer than you are comfortable wearing in the same environment
  • babies get fevers for the same reasons as older children, but they are not quite as good at fighting off infections
  • some babies may have an unstable temperature with an infection – they may be colder than normal. In a sick infant this is a worrying sign. It is a reason to see a doctor urgently
If your child is under three months old and has a fever, they should be checked by a doctor. 
 
If your child is under three months old and you are worried about them, they should be checked by a doctor, even if they do not have a fever.
 

Where to go for more information

This website tool, for babies under six months old, might help guide you as to whether you need to take your baby to a doctor. The website has been designed by a neonatal doctor. The other areas of this website (NICU Tools) are aimed at health professionals.

National Health Service (NHS) Choices. UK

See the NHS Choices website for:

Telephone advice - Healthline and PlunketLine

  • ring PlunketLine on 0800 933 922 if you have child health and parenting questions or queries. For example, if you have questions about such issues as parenting, crying, sleeping, your child's growth, development, behaviour, immunisation, breastfeeding, nutrition, oral health, safety or want to know more about the Well Child / Tamariki Ora programme
  • call Healthline on 0800 611 116 if you need advice about a child of any age who is unwell or hurt, or has any symptoms of sickness. Healthline provides a full range of telephone triage and health advice for children (and adults)
  • both services are available 24 hours and are free to callers throughout New Zealand, including from a mobile phone
This page last reviewed 13 November 2012
© Paediatric Society of New Zealand and Starship Foundation 2005 – 2014
Printed on 26 October 2014. Content is regularly updated so please refer to www.kidshealth.org.nz for the most up-to-date version
Content endorsed by the Paediatric Society of New Zealand