A fever by itself does not mean your child is seriously sick. Check for other signs of your child being unwell, such as a sore throat or diarrhoea (runny poo). If your child looks unwell and you are worried, take them to a doctor whether they have a fever or not.

A quick and easy way to find out whether your child has a fever is to take their temperature using a thermometer.

What is a fever?

The normal body temperature is 37 degrees Celsius (ºC). A mild fever is above 37.5ºC and a high fever is 40ºC and above.

• Fevers are not usually harmful unless they reach 42°. 
• However, babies under 3 months of age with a temperature above 38ºC do need to be checked by a doctor.
• Older children with a temperature above 40ºC should also be seen by a doctor.

What causes fever?

Fever is the body’s natural response to a viral or bacterial infection. Raising the temperature inside the body helps to kill the virus or bacteria causing the infection. Common causes include:

• Chest infections such as bronchiolitis.
• Ear infections.
• Urinary tract infections.
• The flu.
• Common childhood illnesses such as chickenpox.
• Immunisation can also sometimes cause mild fever.

Bacterial infections can be treated with antibiotics but viral infections, which are far more common, do not need antibiotics.

When to see a doctor 

Babies under 3 months old with a temperature over 38ºC should always be seen by a doctor. They are not as good as older children at fighting off infection and are at greater risk of becoming seriously unwell. 

Older children with mild fever (less than 40ºC) do not usually need medical attention unless the fever does not go away in a few days or is associated with other symptoms such as:

• sore throat
• having frequent, watery poo
• complaining or crying when doing wee
• becoming unwell after recent overseas travel
• is not improving after 2 days
• look like they are getting sicker or you feel really worried.

Check with your doctor or phone Healthline on 0800 611 116 if you are worried. If your child has already seen a doctor but they are getting worse, you should take them back for another check.

Will fever harm my child?

Your child might be hot and miserable, but having a high temperature is unlikely to cause any ongoing problems.

Between 2 and 5% of children under the age of 5 may have seizures or fits known as febrile convulsions when they have a fever. These can look alarming but are unlikely to cause long-term harm.

If your child has a febrile convulsion, make an appointment for them to see their doctor afterwards for a checkup. If the convulsion lasts longer than five minutes or your child is having trouble breathing you should phone 111 for an ambulance.

How do I take a child's temperature?

If your child feels hot and grizzly and seems unwell, you can measure their temperature using a digital thermometer. 

Digital thermometers are easy to read and can be used in all age groups. Children under 5 years of age can have their temperature measured in the armpit, older children in the mouth.

Follow the instructions that come with the thermometer. They need to be turned on and some will beep while measuring while others will beep when finished reading. Aim to keep the thermometer in place for two minutes, as a general guide.

Other types of thermometers

• Ear thermometers (electronic or infrared) are expensive and not suitable for use in small babies.
• Mercury thermometers (old-style thermometers) can be dangerous if they break due to their mercury content, so are best replaced with the newer digital options.

How to look after a child with fever

If your child has a fever but is content, eating, drinking and playing, you do not need to do anything. Remember the fever is helping your child fight infection.

If your child is not comfortable encourage them to rest. Make sure their room temperature is comfortable (not too hot or too cold). If possible, open a window for ventilation but avoid draughts. Use a lukewarm flannel to wash the face, hands and neck.

Keep your child in lightweight clothing and bedding – such as a singlet and pants covered by a sheet. Put more clothes or a blanket if your child feels chilled and remove the clothes or blanket when they feel warmer. Change the bed linen and clothing regularly. Do not use hot water bottles or electric blankets during fever.

Encourage your child to drink lots of fluids ie, water, or diluted fruit juice or cordial – little and often is best. If they are hungry offer small healthy meals.

Do I need to give medication for fever?

Medication is not needed for mild fever, but paracetamol can be used if your child is in pain and seems distressed. 

• Use correct doses as listed on the product and measure children’s doses accurately. 
• Do not give for more than two days without seeing your family doctor.
• If your child seems well and is content, there is no need to treat a fever with paracetamol.
  

If needed, how much paracetamol should I give?

The usual dose is 15mg of paracetamol per kg of body weight, no more often than 4 hourly, no more than 4 doses per day.

• For example, if your child weighs 10kg: 15mg x 10kg = 150mg 4 hourly. 
• Do not give regularly for more than two days. See your GP if they are still feverish.

Paracetamol liquid comes in two strengths: 120mg/5mls and 250mg/5mls.

• Please check that you are giving the right dose for the strength you have.
• Make sure that medicines always have a child proof cap and that bottles are stored out of reach.

Medications not suitable for children

• If you have been given ibuprofen for your child, don't use it as well as paracetamol. Use one or the other and only if your child is miserable or complaining of headache or other pain.
• Cold and flu medicines are not recommended for babies and children.
• Do not give aspirin to children under 16 years as it can cause Reye’s syndrome.

Fever after immunisation

Infants and children may have a mild fever after receiving vaccinations. However, it is not recommended to give them paracetamol routinely before or after a vaccination as it may make the vaccination less effective. Ask your doctor or practice nurse for more information.

Learn more

Fever in children Healthed (NZ), July 2014
Fever Kidshealth (NZ), Nov 2012
Febrile convulsions Kidshealth (NZ), Sept 2015
How to take a temperature Kidshealth (NZ), Sept 2013