Temperature, fever

Immune system

Normal body temperature is 37°C or 98.4°F, anything higher means the person has a 'temperature' or what is also know as fever or pyrexia. A high temperature is usually a sign that the body is fighting an infection.

In most cases when the oral temperature is 37.8°C (100°F) or over, fever is present. Temperatures of 40°C (104°F) or over are common in serious illnesses. Temperatures as high as 41.7°C (107°F) or higher are sometimes reached when diseases are in critical stages.

A raised temperature is often the result of a bacterial or viral infection, such as those causing the common cold or flu (influenza). In some cases, it may be a sign of more serious infections such as measles, chickenpox or meningitis.

The person affected may feel hot or cold, sweaty or shivery. Children will feel hot, may be grizzly, miserable or look flushed. Small babies may seem very sleepy, listless and not want to feed.

The most accurate way of checking a person's temperature is to use a thermometer. Standard household thermometers are not suitable for measuring body temperature, purposely designed medical or clinical thermometers are used instead. These include:
Mercury thermometers - these used to be the most commonly used but are gradually being phased out because mercury is dangerous when it escapes if the thermometer breaks. The thermometer is placed under the tongue or armpit for a few moments to give sufficient time for the mercury level to change. Nothing should be eaten or drunk before using the thermometer as this will cause a false reading of the body temperature if the thermometer is placed under the tongue.

Strip-type thermometers - may be used to measure the temperature of babies and young children. The strip-type thermometer is placed on the forehead and any change in colour is noted. As strip-type thermometers measure skin temperature rather than body temperature they are not very accurate, but will at least show if the child's temperature is above normal.

Anal thermometers - are more often used on the continent than in the UK, but are very accurate, and can be safely used with small children and even babies. Anal thermometers show a slightly higher temperature reading than a thermometer placed in the mouth or under the arm as they record the temperature inside the body.

Ear thermometers - are placed briefly in the ear and give an accurate recording of body temperature.

Adults can take regular doses of paracetamol, aspirin or ibuprofen to lower body temperature when there is a slight fever (38°C to 39°C). Children can be given the recommended dose of infant paracetamol or ibuprofen preparations, but must not be given aspirin containing preparations if they are under 16 years of age.

Sponging the forehead with cool or lukewarm water will help reduce body temperature as the water evaporates.

All people, but especially babies and young children, should drink plenty of water or fruit juice to prevent dehydration.

The room temperature should be kept constant and at a comfortable temperature, ie not too cold or too hot.

If the body temperature is very high, 40°C (104°F) or over, medical advice should be sought as soon as possible, particularly if babies or children are affected.

When to see your pharmacist
It is a wise precaution to have a thermometer in the house, particularly if there are children in the family. Talk to your pharmacist about the type of thermometer suitable for your family and for advice on how to use it properly.

Your pharmacist will also advise you on which paracetamol or ibuprofen products to keep close at hand in the home to treat high temperatures as soon as they occur.

When to see your doctor
Contact your doctor immediately if your temperature reaches 40°C or 104°F, if there is a stiff neck, cramps or vomiting, or if a child seems weak and listless or suffers a fit or convulsion. Some people whose immune systems do not work normally will be warned to consult their doctor if they have a raised temperature. Seek medical advice immediately if any baby or child shows signs of meningitis.

Useful Tips
  • Drink plenty of fluids
  • Keep the room at a comfortable temperature
  • Sponging with cool or lukewarm water can help

Reviewed on 27 July 2011

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