Fever in children

Key points

1. Fever is usually caused by your body fighting a viral or bacterial infection. A normal temperature is usually around about 37 degrees Celsius but may be as high as 38 degrees or even higher in some circumstances, and depends on how the temperature is measured and what time of day it is.
2. A baby under 3 months with a temperature above 38ºC, and older babies aged 3 to 6 months with a temperature above 39ºC, should be seen by a doctor. Children with fever lasting for more than 5 days should also be checked by a doctor.
3. If your child has a fever and any of these warning signs, see your doctor urgently: rash, unusual sleepiness or floppiness, pain, irritability or persistent crying, inability to swallow, breathing difficulty, persistent vomiting or not drinking fluids well.
4. If your child looks unwell and you are worried, take them to a doctor whether they have a fever or not.
5. You can treat most fevers at home with rest, fluids and generally keeping your child comfortable. Painkillers, such as paracetamol or ibuprofen, are not needed unless your child is distressed.

What are the signs of fever?

The normal body temperature is between 36.5ºC–37.5ºC. Fever is when body temperature is raised above this, usually because the immune system is active fighting off a virus or bacterial infection. The best way to find out whether your child has a fever is to take their temperature using a thermometer.

• Mild fever (37.5–38.5°C) – your child might have flushed cheeks, feel a little lethargic and be warm or hot to touch. They will generally be able to do their normal daily activities.
• High fever (38.5–39.4°C) – your child will feel hot to touch. They may not feel well enough to do their usual activities, have reduced appetite and may have aches and pains.
• Very high fever (39.5°C or higher) – your child will usually want to stay in bed or be inactive; they won’t feel well enough to do their normal activities. They will feel hot to touch and may have lost their appetite. 

Note: If you use a rectal thermometer, temperatures might be higher by 0.5 degrees than these ranges.

When to see a doctor

• A baby under 3 months with a temperature above 38ºC needs to be checked by a doctor.
• Older babies aged 3 to 6 months with a temperature above 39ºC should be seen by a doctor.
• Children with fever lasting for more than 5 days should also be checked by a doctor.
• If your child has a fever and any of these warning signs, see your doctor urgently: rash, unusual sleepiness or floppiness, pain, irritability or persistent crying, inability to swallow, breathing difficulty, persistent vomiting or not drinking fluids well.
• If your child looks unwell and you are worried, take them to a doctor whether they have a fever or not.
• It‘s also important to look at other symptoms and how unwell your child seems. Some mild diseases produce very high fevers and severe illnesses can produce mild fever.

What causes fever in children? 

Fever is the body’s natural response to an infection somewhere in the body. Some types of infections that can lead to fever include:

• infections caused by viruses – most children (9 out of 10) with a fever have a viral illness such as a cold, flu or tummy bug (gastroenteritis)
• infections caused by bacteria, such as some ear infections, chest infections or urinary tract infections.

Immunisation can also sometimes cause mild fever. However, it is not recommended you give children paracetamol routinely before or after a vaccination as it may make the vaccination less effective. Wrapping a baby in too many warm layers of clothing or bedding can also cause a fever. 

How do I look after a child with a 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, you can do the following:

• encourage them to rest 
• encourage them to drink lots of fluids, especially water – little and often is best
• if they are hungry offer small healthy meals
• make sure their room temperature is comfortable and steady (not too hot or too cold)
• use a cool cloth to wash their face, hands and neck.
• don’t use any rapid cooling methods that make your child shiver
• keep your child in lightweight clothing and bedding, such as a singlet and pants covered by a sheet
• change the bed linen and clothing regularly
• do not use hot water bottles or electric blankets
• check your child during the night
• take them to the doctor if your child doesn’t seem to improve or you’re at all worried (see when to see a doctor).

Should I give my child painkillers for fever?

• Paracetamol: can be used for children older than 1 month to make them more comfortable. The dose of paracetamol is based on your child’s weight and not their age. Read more about how to give paracetamol to babies and children.
• Ibuprofen: can be used for children older than 3 months but only if your child has a fever and is miserable. Ibuprofen may be effective at reducing fever, but can damage the kidneys, especially if they are dehydrated, so should be used carefully. Read more about ibuprofen for children.
• Paracetamol and ibuprofen: should not be given at the same time.

Other medicines

• Cold and flu medicines: not recommended for babies and children.
• Aspirin: never give your child or young person aspirin as this may increase the risk of Reye's syndrome, which is a rare and serious illness.
• Antibiotics: only work to kill bacteria. Most children with fever do not have a bacterial infection, so antibiotics will not help them.

Learn more

Fever KidsHealth, NZ, 2015
Fever in children Ministry of Health, 2018

References

1. Fever in adults  Ministry of Health, NZ, 2017
2. Treating fever in children Choosing Wisely, NZ, 2018
3. Fever and night sweats Patient Info, UK, 2015
4. Identifying the risk of serious illness in children with fever BPAC, NZ, 2010

Reviewed by

Dr Jonathan Kennedy is a senior lecturer in the Department of Primary Health Care & General Practice at the University of Otago, Wellington, a general practitioner in Newtown, Wellington, and a Medical Officer at Regional Public Health, the Wellington region public health unit. He has a special interest in the primary health care needs of refugee and migrant arrivals to New Zealand. He graduated with an MBChB (Otago) in 1997 and subsequently completed postgraduate diplomas in Obstetrics, Paediatrics and Public Health. He has been a fellow of the Royal New Zealand College of General Practitioners since 2007.