[David Anderson]

David Anderson  asked the Naked Scientists:

Dear Chris,

With the average human body temperature of 98.6 degrees F or 37 degrees C, why is it that when the outside air temperature is 100 degrees F we humans feel so hot? We should feel perfect, that's our body temperature.

Thank you,
David
Central California, USA


What do you think?

[chris]

It's all to do with our thermoreceptors - the chemical nerve detectors that tell the brain how warm we are. The body is set up to maintain a steady temperature by balancing heat loss and heat production, and this system is optimised for the ambient temperature at which we live.

In other words, our heat loss systems work well at air temperatures of 0-30 degrees; but once you exceed this temperature it becomes much more difficult for the body to lose heat efficiently. As a result there is a risk of over-heating.

To prevent this, we are set up to be sensitive to temperatures lower than our limit so we take avoiding action earlier rather than later to cool down.

37 degrees may be our body temperature, but that's the temperature of the body AFTER it has produced a huge amount of heat from the metabolic reactions occurring in every cell in every tissue and after it has compensated for heat loss to the environment.

Consequently, if you are in air of the same temperature as body temperature it becomes very hard to lose heat and we begin to overheat.

Chris