Measuring body temperature is very important in medicine. A number of diseases are characterised by a change in body temperature. With other illnesses, the course of the disease can be followed by measuring body temperature. This allows the doctor to analyse the effectiveness of treatments based on body temperatures.

A fever is the reaction to a disease-specific stimuli. The body changes its normal temperature to support the body’s own defence mechanisms. Fever is the most common form of disease-related (pathological) increase in body temperature.

The measured body temperature always depends on which part of the body the measurement was taken from. For this reason, and contrary to popular opinion, there is no general normal temperature.

The body temperature of a healthy person also changes throughout the day and depending on what activities they undertake. With a rectal temperature measurement, the body temperature is normally 0.5 degrees Celsius higher in the evening than other times of the day for physiological reasons. In addition, body temperature is increased by any physical exertion.

A fundamental distinction is made between:

• Core temperature: made by inserting the thermometer into a bodily orifice and provides the temperature of the mucous membrane.
• Surface temperature: measured on the surface of the skin and is made up of the temperature inside the body and the ambient temperature.