Fever

Also known as a high temperature

Fever is when your core body temperature is raised above the normal 37 degrees Celsius.

This page provides general information about fever. If you have a child with a fever, see fever in children.

Key points

  1. A fever is usually caused by your body fighting a viral or bacterial infection.
  2. On its own, a fever does not mean you are seriously sick, but it’s important to check for other signs of illness.
  3. A fever usually lasts 3 to 5 days and most people will recover from a mild fever with self-care at home.
  4. Pregnant women and young babies with a fever need to see a doctor.

What are the symptoms of a fever?

Mild fever (38–38.9°C)

With a mild fever you might have flushed cheeks, feel a little lethargic and be warm to touch. You will generally be able to carry out normal daily activities. 

High fever (39–39.9°C)

With a high fever, you’ll feel hot to touch. You may not feel well enough to go to work and you may have aches and pains. 

Very high fever (40°C or higher)

With a very high fever, you will usually want to stay in bed or be inactive – you won’t feel well enough to carry out normal activities. You’ll feel hot to touch and you may have lost your appetite.

When to see a doctor

Young babies and pregnant women

Babies under 3 months old with fever must be checked by a doctor, and babies between 3 and 6 months with a high or very high fever (anything over 39ºC) must also be taken to the doctor. Read more about fever in children.

If you’re pregnant and have a temperature of 38.5ºC, or any fever lasting for 3 days or more, see your lead maternity carer. They need to monitor the effects of the fever on your baby.

Other ages

Older infants, children and adults will not usually need any medical treatment for mild fever, especially if you are otherwise well.

However, you should see your doctor if you:

  • have a very high fever (over 40ºC)
  • are still feverish after 3 days of home treatment or seem to be getting sicker
  • are shivering or shaking uncontrollably, or have chattering teeth, and it doesn’t stop within an hour or so
  • have a severe headache that doesn’t get better after taking painkillers
  • are having trouble breathing
  • are getting confused or are unusually drowsy
  • have recently travelled overseas.
See your doctor or go to an emergency department immediately if you notice the following symptoms (along with a fever): 
  • severe headache
  • stiff neck
  • sensitivity to light.

These symptoms may indicate meningitis, which needs urgent medical attention.

Phone Healthline on 0800 611 116 if you are worried and unsure what to do. If you have already seen a doctor but your symptoms get worse, go back for another check.

What causes fever?

Fever is usually caused by a viral or bacterial infection. Fever is your body's way of fighting infection. Raising the temperature inside your body helps to kill the virus or bacteria causing the infection. 

Common conditions that can cause fevers include:

A mild fever may be experienced after receiving a vaccination. However, it is not recommended that you use paracetamol routinely before or after a vaccination as it may make the vaccine less effective.

Do I need medication for fever?

Fever is your body’s way of fighting infection. Medication is not needed for mild fever, but you can use paracetamol if you also have a headache, pain or distress. 

How do I care for myself with fever?

  • Drink plenty of fluids, especially water (little and often is best). Aim for 2–3 litres in 24 hours while you have a fever. Tea and coffee can help you feel better during the day, but don’t drink them in the evening as they may interrupt your sleep.
  • Get plenty of rest. Sleeping for 2–3 hours at a time is slightly better than just resting.
  • Make sure the room temperature is comfortable (not too hot or too cold).
  • If possible, open a window for ventilation but avoid draughts.
  • Wear lightweight clothing and use lighter bedding.
  • Do not use hot water bottles or electric blankets.
  • Use a cool cloth to wash face, hands and neck.
  • Change bed linen and clothing regularly. 

Learn more

Fever Mayo Clinic, US
Influenza Ministry of Health, NZ, 2018

References

  1. Fever in adults  Ministry of Health, NZ, 2017
  2. Fever and night sweats Patient Info, UK, 2015
  3. Cold season – managing without antibiotics BPAC, NZ, 2018
Credits: Health Navigator Editorial Team. Reviewed By: Dr Marion Leighton, Consultant physician, Wellington Hospital Last reviewed: 27 Feb 2015