What is a fever?
A fever occurs when the body temperature rises above normal. The normal body temperature is between 36 and 37°C, but this can vary from person to person and from hour to hour. Temperatures between 37.5°C and 38.2°C mark a low-grade fever. A high-grade fever is present when the oral temperature is above 38.2°C.
The method by which the temperature is measured can also affect the reading. A fever is generally accepted to be present in children if:
- the axillary (armpit) temperature is higher than 37°C;
- the oral (mouth) temperature is higher than 37.5°C; or
- the rectal or tympanic (ear) temperature is higher than 38°C.
What causes fever?
Fever results from the ‘thermostat’ in the brain being reset at a higher temperature than normal. This happens through the release of chemicals when the immune system is activated, generally by a bacterial or viral infection. Fever is part of the body’s way of fighting infection.
Immunisation, severe sunburn, autoimmune disease such as rheumatoid arthritis, and other conditions can also sometimes cause fever. There are also a number of factors that may cause a higher than normal temperature including physical activity, emotional stress and ovulation.
How do I take a temperature?
- Shake down the mercury in the thermometer, so that it falls below the 35°C line, or press reset on a digital thermometer.
- Place the silver tip or thin end of the thermometer high in the armpit. It is important that the thermometer remains in the right place.
- In older children or adults, the thermometer may be placed under the tongue, but great care must be taken to avoid biting or breaking the bulb.
- Leave in place for at least 2 minutes for a mercury thermometer or until it beeps for a digital thermometer.
- Read the thermometer by gently rotating it between your thumb and forefinger. The temperature is measured by looking at the level of the silver bar which runs up the middle of the thermometer. If you cannot read this type of thermometer, you can buy a thermometer which has a digital read-out on the side.
- Wipe the thermometer with antiseptic or lukewarm soapy water. Do not use hot water or you will break the thermometer.
- Battery operated tympanic (ear) thermometers are also available. These are placed gently in the ear canal and read the temperature from the ear drum. The advantage of tympanic thermometers is that they are very quick, giving a reading in a few seconds; however, they are not always accurate.
When to see the doctor
Infants 6 months old or younger should be taken to a doctor if they develop a fever.
If an infant older than 6 months or an older child has a fever, take them to a doctor if you are concerned, or if the child:
- seems very ill;
- has an earache;
- has a stiff neck;
- cannot swallow normally;
- has a rash;
- is breathing faster than normal;
- is vomiting;
- is passing less urine than normal;
- is very drowsy or sleepy; or
- has a bulging fontanelle (the soft spot on a baby’s head).
While the child has a fever, monitor them every 4 to 6 hours for the above symptoms and take them to a doctor if any of these symptoms occur.
Take or return an adult with a fever to the doctor if they:
- have a severe headache or neck pain;
- have pain elsewhere in the body (especially the ears);
- have not had anything to drink for 8 to 10 hours or are constantly vomiting;
- say that light hurts their eyes;
- have a rash;
- have not improved after 48 hours;
- have difficulty waking up; or
- look like they are getting sicker or you feel really worried.
Treating a fever
Follow your doctor’s advice carefully about home care, changes in the person’s condition and what to do if they get worse after hours. If the doctor thinks a bacterial infection is causing the fever, antibiotics may be prescribed. However, be aware that many infections are caused by a virus, in which case treatment with antibiotics is not effective.
Low-grade fever itself is not generally harmful and may even help your body eliminate a virus. So if no other problems are present, your doctor may advise supportive measures such as drinking plenty of fluids and resting rather than any medical treatment.
If you or your child have a fever and are uncomfortable, vomiting, dehydrated or having trouble sleeping, your doctor may recommend the following methods to make you more comfortable and to reduce the fever.
- Keep clothes and blankets to a minimum. If you are shaking and feel cold, cover up with blankets until the shakes stop, then promptly remove the blankets. Shaking is the body’s way of cooling down when it is very hot.
- Avoid hot water bottles or electric blankets. Make sure the room temperature is comfortable.
- Open a window for ventilation but avoid draughts.
- Drink plenty of clear fluids — aim for one glass every hour. A drink such as Gastrolyte or Hydralyte, which helps replace the body’s electrolytes, may be beneficial if you have vomiting or diarrhoea. Ice-blocks are useful for children.
- A lukewarm flannel-bath can be refreshing. Fill a large basin or bucket with lukewarm water, and using a flannel, wash the face, hands and neck. Do not use cold water, as this can increase core body temperature by causing shivering.
- Change the bed linen and clothing regularly.
- Adults can take aspirin, paracetamol or ibuprofen for relief.
- Children can take children’s formulations of paracetamol (some formulations can be given to children older than one month) or ibuprofen (some formulations can be given to children older than 3 months, but ask your doctor for advice for infants younger than one year). Ask your doctor or pharmacist for advice on the right dose for your child.
- Do NOT give aspirin to infants or children unless specifically told to by your doctor.
Last Reviewed: 19 March 2010
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