Core temperature is that deemed to be perfusing vital organs such as the brain and heart; it is usually maintained at 36-37.5 degrees centigrade. It is measured clinically from probes in the rectum, oesophagus or nasopharynx.
Practically, this sort of measurement is difficult, and so oral, usually sublingual, temperature is recorded. The core temperature is not maintained to the superficial layers of the body which are cooler, and have a wider range of temperature variation with changing external temperature. Hence, oral temperature is usually 0.25 to 0.5 degrees centigrade lower than core temperature.
The core temperature exhibits a circadian rhythm, being lowest in the early hours of the morning, and a monthly rhythm in females in tandem with ovulatory cycles.
Last reviewed 01/2018