Fever is defined as a body temperature above 37 °C. Normal body temperature measured rectally is 36.3 °C to 37.8 °C. Fever is generally the body's reaction to infections. Fever accelerates metabolic processes and inhibits the increase of bacteria and viruses.

The different thermometers are suitable for measuring body temperature in different parts of the body.

• Forehead thermometer: measurement only on the forehead
• Ear thermometer: measurement only in the ear
• Rod thermometer: rectal (in the back passage), axillary (under the arm) or oral measurement (in the mouth).

The temperature varies depending on the part of the body where the measurement is taken. The difference in healthy persons between different parts of the body can be between 0.2–1°C.

The approximate normal temperature ranges are as follows:

• Forehead temperature – measured with a forehead thermometer: 35.8°C to 37.6°C.
• Ear temperature, measured with an ear thermometer: 36.0°C to 37.8°C.
• Rectal temperature, measured with a conventional thermometer: 36.3°C to 37.8°C.
• Orally measured temperature – measured with a conventional thermometer: 36.0°C to 37.4°C.

Temperatures measured with different thermometers cannot be compared with one another. You should therefore tell your doctor or bear in mind if you are diagnosing yourself what thermometer you used to take your temperature and in what part of the body.

• The person’s individual metabolism
• Age (body temperature is higher in babies and small children and falls with increasing age. Greater temperature fluctuations occur faster and more often in children)
• Clothing
• The outside temperature
• The time of day (body temperature is lower in the morning and increases during the day towards evening)
• Preceding

Tip: Taking the temperature gives a measurement that provides information about a person’s current body temperature. If you are uncertain about interpreting the results or if the result is abnormal (e.g. fever), you should consult your doctor. This also applies in the case of slight temperature changes if there are other symptoms of illness such as agitation, severe sweating, flushed skin, fast pulse rate, tendency to collapse etc.