Fever

Also known as a high temperature

Fever is when your core body temperature is raised above 37.5 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 about fever

  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 urgently for fever. 

What is a fever?

Fever is when your core body temperature is higher than 37.5 degrees Celsius. Usually, you will feel unwell and hot, and you may sweat. Sometimes you will feel very cold and shiver even when your temperature is high.

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

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

When should I seek help for my fever?

Most fevers aren't life-threatening, but sometimes you need to seek medical advice.

If you’re pregnant and have a fever, 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 with a fever: 
  • severe headache
  • stiff neck
  • light hurts your eyes.

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 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?

A viral infection is the most common cause of a fever. A bacterial infection is less common but is more serious. Your body's natural reaction to infection is to raise your body temperature. This helps kill the infection. Vaccination sometimes causes a mild fever too.

Do I need medicine for fever?

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

How do I care for myself with fever?

  • Drink plenty of fluids, especially water or rehydration fluid (little and often is best). Aim for 2–3 litres in 24 hours while you have a fever. 
  • Get plenty of rest.
  • 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 your face, hands and neck.
  • Change bed linen and clothing regularly, especially if they are wet from sweat. 

Learn more

Fever Mayo Clinic, US
Influenza Ministry of Health, NZ

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

Reviewed by

Dr Sharon Leitch is a general practitioner and clinical research training fellow in the Department of General Practice and Rural Health at the University of Otago. Her area of research is patient safety in primary care and safe medicine use.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Sharon Leitch, GP and clinical research training fellow, University of Otago Last reviewed: 18 Sep 2020