Fever – general

Also known as a high temperature

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

COVID-19 pandemic

If you have any respiratory symptoms such as a cough, sore throat, shortness of breath, head cold or loss of smell, with or without fever, call your GP or Healthline's dedicated COVID-19 number 0800 358 5453 to check whether you need to be tested for COVID-19.

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 an infection.
  2. On its own, a fever doesn't mean you are seriously sick, but you need to check for other signs of illness.
  3. A fever usually lasts 3–5 days and most people recover from a mild fever with self-care at home.
  4. However, there are times when you should see a doctor for fever, or see one urgently – see below for details. 

What is a fever?

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

Mild fever: You have a mild fever if your temperature is higher than 38ºC.
High fever: A high fever usually means more than 39ºC.

You find out how high your temperature is by using a thermometer. Read more about thermometers and how to use them.

When should I seek help for my fever?

Most fevers aren't in themselves life-threatening, but there are times where you need to seek medical advice.

If you’re pregnant and have a fever of over 38°C, you may have a virus, so check with your midwife, doctor or nurse before you take any medicines. If your fever lasts for longer than a day, check with your midwife, doctor or nurse.

When should I see a doctor urgently?

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.

Contact your doctor immediately if you have a fever and you are:

  • on treatment for immune deficiency
  • taking immune-suppressant medicines such as steroids, methotrexate or cancer medication
  • a transplant recipient
  • HIV positive.

Phone Healthline on 0800 611 116 if you are worried and not sure what to do. If you have already seen a doctor but your symptoms get worse, go back for another check.

When should I see a doctor?

You should see your doctor if you have a fever and have the following underlying conditions:
  • ongoing lung problems such as COPD, bronchitis or asthma
  • ongoing gastrointestinal or liver disease 
  • cystic fibrosis
  • chronic kidney disease
  • sickle cell disease.

You should also 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 pain medicines
  • are having trouble breathing
  • are getting confused or are unusually drowsy
  • have recently travelled overseas.

What causes fever?

The most common cause of a fever is a viral infection. A bacterial infection is a less common but more serious cause. Your body's natural reaction to infection with a virus or bacteria is to raise the temperature inside your body. This helps to kill the infection. Another cause of raised body temperature is vaccination, which usually causes only mild fever.

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 droughts.
  • Wear lightweight clothing and use lighter bedding.
  • Do not use hot water bottles or electric blankets.
  • Use a cool cloth to wash your 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
  4. Danger signs during pregnancy Ministry of Health, NZ, 2017
  5. Fever in adults NHS Inform, UK, 2020
Credits: Health Navigator Editorial Team. Reviewed By: Dr Marion Leighton, consultant physician, Wellington Hospital Last reviewed: 15 May 2018