Fever is usually the result of an infection

Fever is not an illness but is a common symptom of viral and bacterial infections.

In addition to a high temperature, fever can occur with symptoms including:

  • Flushed and warm skin
  • Sweating or shivering
  • Headache
  • Muscle aches
  • General tiredness or feeling weak
  • Loss of appetite

An infection isn’t always the reason you get a fever. A fever can also be caused by reactions to medicines or inflammation.

How fever fights infection

Fever is your body’s weapon against infection.

Your body temperature is controlled by a part of your brain called the hypothalamus. It’s a bit like a thermostat – when you’re healthy, the hypothalamus sets your body to a normal temperature of about 37°C.

But when you’re sick with an infection, your immune system releases chemicals that make the hypothalamus reset your body to a higher temperature. You begin to feel cold and you may start to shiver, causing you to bundle up in warmer clothing. All of this causes your body temperature to rise to the new higher setting.

This rise in body temperature helps to fight the viruses and bacteria that cause infection.

When is a high temperature too high?

A normal body temperature is around 37°C, although this can vary slightly from person to person and can be affected by factors such as age, time of day, activity, and eating.

In general, a temperature of 38°C or higher is considered a high temperature and you may experience symptoms of a fever. Fevers are often graded as mild (38°C–39°C), high (39°C–40°C), and very high (40°C or above).

However, some mild illnesses can result in high fevers and some more serious illnesses only cause mild fevers. So it’s important to consider other signs and symptoms that may occur with your fever.

Practical ways to reduce a fever

Most fevers usually go away within 3 to 4 days. A mild fever may not need any treatment.

To help relieve the discomfort of fever, you can:

Get plenty of rest

Drink plenty of fluids, especially water

Stay cool by wearing light clothes and sleeping with light bedding

Place cool cloths on face, neck, and arms, but avoid any form of rapid cooling that causes shivering

Take a fever-reducing medication such as ibuprofen or paracetamol

Signs you should see a doctor

Most fevers are nothing to worry about and usually go away within a few days. However, you should seek immediate medical advice if you experience any of the following:

  • Temperature 40°C or higher
  • Fever that lasts more than 3 days or gets worse
  • Chills or uncontrollable shivering
  • Feeling confused or unusually drowsy
  • Severe headache or stiff neck
  • Difficulty breathing or shortness of breath
  • Rapid heartbeat or rapid breathing
  • Hallucinations
  • Vomiting
  • Skin rash
  • Seizure, or regular twitching or jerking

You should also seek medical advice if you have recently travelled overseas or to an area where any infectious disease is common or if you have been exposed to someone with or suspected of having COVID-19.