[thedoc (OP)]

Jess González asked the Naked Scientists:
   
Why is it our body's appropriate temperature is 98.6, yet when the temperature in the air is 98.6, we are extremely hot?

What do you think?

[evan_au]

Humans generate heat, as part of our normal metabolism. We have to get rid of that heat, or we die of hyperthermia (heat exhaustion).

Human enzymes and biochemical reactions are optimized to operate best at around 98F/37C, and this is the normal temperature of the human core. If the core gets much hotter (or colder) than this, reactions don't work so well, and we die. So humans have many mechanisms to maintain core temperature at this ideal, such as opening or closing capillaries in the skin, sweating, wearing clothes or putting up an umbrella, etc.

Heat naturally flows from a hotter object to a colder object, so to keep the human core at 98F/37C with minimum effort, you need an air temperature of around 75F/25C.

If the air temperature reaches 98F/37C, the heat generated by our metabolism will not flow to the outside air by itself, so it's hard to get this heat out. This means sweating, opening capillaries, going into a cool house and/or taking a siesta so you don't generate so much heat.

The worst combination occurs in hot and humid tropical countries. If the humidity is near 100%, sweat does not evaporate. This breaks the most effective natural means we have of dissipating heat: sweating. This leaves you feeling exhausted.