Fever facts- the causes and when to worry

When is a fever serious?

Fever is a common symptom- and it can cause a lot of worry. There are a few questions patients commonly ask doctors when they have a high temperature- what it means and what to do about it. So, here are a few facts and figures to make matters a little clearer:

What controls body temperature?

A part of the brain called the hypothalamus controls body temperature- basically it’s the body’s thermostat- and it can reset the body to a higher temperature during infection and other illnesses

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What number means I’ve got a fever?

It depends how it’s measured. If measured in the ear or under the arm, the cut-off point is 37.2C (99.0 F), while in the mouth it’s 37.7C (99.9F). There is a range of “normal” however, which varies depending on age, gender, time of day, physical activity and other factors. In children, temperature can naturally vary a little more than in adults- according to the Royal Children’s Hospital in Melbourne a fever in a child is defined as body temperature above 38C.

Can a high temperature be a good thing during an infection?

There is some controversy over this issue- in theory, a fever may actually be helping the body to fight infection. Some parts of the body’s immune system, such as white blood cells, may work better at a higher body temperature. It also seems that some bacterial infections may be slowed down when body temperature is higher.

So does this mean I shouldn’t treat a fever with medication every time?

While a fever may be a useful defence against infection, research suggests that treating a fever with medicine such as paracetamol doesn’t make a difference to the overall outcome. Your doctor is likely to advise a common sense approach. So, if you have a fever and are feeling out of sorts, these medicines are worth trying and may make you feel more comfortable. But if you have a low grade fever and feel reasonably well, no treatment is necessary.

Does a higher fever always mean a more severe illness is present?

Not necessarily. Doctors always try to look at the bigger picture. A person can have a very high fever with a viral illness which will settle by itself, or they might have a milder fever but have a more serious illness! The history and examination usually clarify matters. The important thing is to see a doctor if you feel quite unwell, or if a fever is not settling after a few days.

When should I worry about a fever in a child?

The Royal Children’s Hospital recommends that parents bring their child to see a doctor if they have a fever and are under the age of three, if they complain of stiff neck or that the light is hurting their eyes, if they are vomiting/refusing fluids, if they have a rash, if they are more sleepy or irritable than usual, or if they have difficulty breathing or appear to be in pain. If, as a parent, you are worried or in doubt, it’s always best to seek early advice.

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Can anything other than infection cause a fever?

Yes, though it’s very rare indeed. These unusual causes include blood clots, cancer, or side effects of certain medications. Also, the body can overheat if the external surroundings are too hot leading to hyperthermia or “heat stroke”. This is different from a fever- in a fever the body sets its own thermostat at a higher level, whereas in hyperthermia outside factors (such as hot weather) cause the rise in temperature.

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