It is of great medical importance to measure body temperature. The reason is that a number of diseases are accompanied by characteristic changes in body temperature. Likewise, the course of certain diseases can be monitored by measuring body temperature, and the efficiency of a treatment initiated can be evaluated by the physician. Fever is the most common form of pathological (disease-related) elevation on body temperature.

Essentially, it is true that the measured body temperature always depends on where it is measured. Therefore, contrary to popular consensus, there is no simple "normal temperature. Furthermore, a healthy person's body temperature will vary with activity and time during the day. In a rectal temperature measurement, a typical temperature difference of 0.5°C between the higher evening temperatures is physiological. Body temperature is typically elevated after physical activity.

Roughly speaking, a distinction is made between a core temperature and a surface, where the surface temperature is measured at the skin surface and is a mixed temperature between the body's core temperature and the ambient temperature. The core temperature is measured by inserting a thermometer into a body cavity, which yields the temperature of the mucous tissue.

Essentially a distinction must be made between the technical accuracy of the thermometer itself and the clinical accuracy in use in taking a temperature. The former is determined under idealized conditions to guarantee the quality of the instrument, taking the relevant technical standards into account. An accuracy of + 0.1°C can be considered state of the art for high-grade thermometers.

The user must NOT confuse technical accuracy with this accuracy in use. The human body temperatures described here, which depend on the measurement location and time, are due to physiological causes and are not due to a thermometer malfunction. By correctly applying a thermometer, the accuracy can be strongly increased (follow the operating instructions!)


The most reliable core temperature is obtained by inserting a thermometer into the rectum (rectal measurement). This measurement is accurate and has low scattering in the results. The normal range is approx. 36.6°C to 38.0 °C.


The oral measurement can be performed as a buccal measurement (in the cheek) or as a sublingual measurement (under the tongue). Both measurement underestimate the rectal temperature by approx. 0.3°C to 0.8°C.

The only types of body surface temperature measurement used clinically in practice are the arm pit (axially measurement) and in the groin (inguinal measurement). In both cases, the respective limb is pressed against the body in order to reduce any ambient temperature influence. However, this is successful only to a limited extent with the disadvantage that the measurement time is long. In adults, the axillary measurement is lower than the rectal by approx. 0.5°C to 1.5°C!

In infants, these underestimates in comparison with the rectal temperature are much smaller.

Infrared ear thermometers measures infrared energy radiated from the eardrum and the surrounding tissue; non contact forehead thermometer measures infrared energy radiated from the forehead. This energy is collected through the lens and converted to the correct temperature value.