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What is a fever: when should you worry about a high temperature?

Woman Checking Child's Temperature
Fevers can be distressing when you're worried about your child's health.

When was the last time you had a fever? You probably remember feeling pretty yucky: maybe too hot or cold, or having chills, shivers or sweats. If you’ve looked after a baby or child who has a fever, you’ll know that while fevers can be common in young people, they can be distressing when you can’t explain to your little one what’s going on and you’re worried about their health.

Fevers are a normal bodily function that happens when the body encounters infection, but there are times when a fever requires medical attention. Read on to learn more about what a fever is and when to get help for a fever when you, or someone you are caring for, are sick.

What is a fever?

Fevers happen when your body temperature rises above normal, usually in response to an infection in the body. This is why people sometimes call a fever a ‘temperature.’

Fevers aren’t actually caused by the infection or illness you have, but are a part of your body’s immune system response, and are a sign that your body is working to make itself better. You might have a fever when you have an illness caused by a virus, like influenza, or a bacterial infection.  

What is a normal or healthy body temperature?

Your body’s temperature will usually be about 36-37°C. A ‘normal’ body temperature can change depending on your age, what you’ve been doing and the time of day; your body temperature might be a little higher if you’ve been exercising, and your body temperature will usually be at its lowest just before dawn and highest in the afternoon.

If you want to find out your normal body temperature, measure your temperature using a thermometer for a few days in a row when you’re feeling well. This will give you a good indication of what temperature your body normally sits at. When you have a fever, your body temperature will be higher than normal. Usually, a temperature over 38°C is a sign of fever.

How to measure body temperature

Body temperature is measured using a tool called a thermometer. These days, thermometers are digital devices, which show the temperature on a screen. In the past, thermometers used a substance called mercury to measure temperature, but these thermometers are no longer used in hospitals or sold to the public.

Follow the instructions on your thermometer to measure body temperature. There are different places on the body where temperature can be measured, including the armpit, ear, under the tongue, or rectum. Your thermometer might be designed to measure temperature in one or more of these spots.

Side effects of fevers

Fevers are rarely harmful, but can make you feel uncomfortable. Ironically, when your temperature is on the rise you might get chills or shivers, while your temperature falling can make you sweaty.

High fevers can cause febrile convulsions (seizures) in children. This happens in about 3% of children aged 6 months to 5 years. Almost all children who get febrile convulsions will outgrow them once they are 4-5 years old. Febrile convulsions don’t cause any long-term health problems, but you should talk to your doctor if your child has one.

When to go to the doctor or ED for a fever?

The seriousness of a fever depends on the age and health of the person who is sick.

If a baby under 3 months has a fever, they need to see a doctor immediately.

In children over 3 months and in adults, a fever can be treated at home. Seek medical attention if the person has any of these other symptoms as well as fever:

  • trouble breathing
  • drowsiness
  • refusing to drink and/or not urinating as often
  • stiff neck
  • sensitivity to light
  • ongoing vomiting or diarrhoea
  • looking sicker than before – more pale, lethargic or weak
  • any other symptoms that are causing you worry.

You should also see a doctor if you or someone you are caring for:

  • still have a fever after three days
  • are shivering or shaking uncontrollably
  • are hot but not sweating
  • are getting sicker instead of feeling better
  • have recently travelled overseas
  • Seek urgent medical attention if a person of any age has a fever with a headache and stiff neck, or has rash that doesn’t blanche (fade) when pressed. You should call an ambulance if you or someone you are caring for has unexpected or unusual symptoms like hallucinations,  muscle spasms or feels confused or drowsy.

If you’re not sure whether a fever is serious and you should see a doctor, you can speak to a registered nurse by calling 13 HEALTH (13 43 25 84) 24 hours a day, 7 days a week.

If you ever think that the situation is an emergency or that someone’s life is in danger, call Triple Zero (000) for an ambulance immediately.

Man sick in bed

How to treat a fever

Most often, fevers can be treated at home. You don’t need medication to treat a fever unless the person who is sick is feeling uncomfortable.

Treat fever by:

  • giving paracetamol or ibuprofen if the person is uncomfortable, following the instructions on the packaging for how much and how often the medication should be given (ibuprofen can only be given to children over 3 months of age)
  • dress in light clothing
  • avoid using heavy blankets or quilts which might make you too hot and increase your temperature
  • drink clear fluids like water and offer breastfed infants more feeds than normal
  • rest

Cold baths, sponges and fans might seem like a good idea when you have a temperature, but they can actually make you feel more uncomfortable and should be avoided.

More information

Fever – Health Direct

Fever and high temperatures in children – Health Direct

Fever – Raising Children

Last updated: 18 February 2019