A normal core body temperature range is between 97°F (36.1°C) to 99°F (37.2°C).
During the day, the temperature fluctuates and this is known as the Circadian Rhythm so the widely regarded temperature of 36.9ºC / 98.4ºF is a daily average and subject to variation.
During sport, the core body temperature can increase above 38ºC / 100.4ºF
Temperatures above 39ºC / 102ºF start to put the human body at risk of heat-stress although the training and conditioning of each individual means that the tolerance varies significantly.
What is reliable temperature measurement?
Different thermometer methods give different core body temperature readings.
Rectal thermometers, ingested e-pills and bladder and heart catheters are all invasive thermometers which are also considered to be accurate and hence are suitable for medical use.
Laser scanners, ear thermometers, oral thermometers and other skin temperature calculators are considered less accurate and consistent so the values delivered by a single device or in comparison to other thermometers can vary significantly. The temperature also varies on different parts of the body (for example, the extremities such as arms and legs can be cooler().
The CORE Body Temperature monitoring device is has been tested extensively using accurate rectal thermometers and e-pills as 'controls' to provide the same level of accuracy.