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The skin knows when things heat up
 Q: Since our body temperature is around 99 degrees, why do we feel hot when the weather hits
the 90s? Since our bodies are hotter than that, it would make sense that any temperature below
99 would feel cool, not hot. Ben R., Buffalo, New York
A: True, our body maintains an internal temperature of about 99 degrees Fahrenheit (37 degrees
Centigrade). However, our skin-together with our body--tells us when we're hot or cold and it's
normal temperature is about 91 degrees.
[Corel] Yugoslav troops descending hot desert sands in Egypt
"...the purpose of the skin thermal sensors is to 'sense' any thermal threat from the environment..." says
Michel B. Ducharme thermal physiologist of Defense & Civil Institute of Environmental Medicine,
Toronto, Ontario. The deep thermal sensors, meanwhile, tell us whether the body temperature is OK.
We sense the surrounding temperature with tiny sensors imbedded in our skin, which are extremely sensitive to changes in temperature.
When these sensors register about 91 degrees and our whole body is at a good temperature, we feel comfortable. Higher than that
means we're getting too hot.
The hypothalamus (a primitive part of our brain) controls the action, like a furnace controller/thermostat-only much more sophisticated.
Signals come in to the hypothalamus from the brain, from deep-body, and skin sensors. The hypothalamus integrates the signals to learn
how warm the deep body is and how the body surface is changing: warming or cooling. Then it decides what to do: OK means do
nothing; otherwise kick off action to get the body temperature right again.
When the hypothalamus decides to cool the body, we sweat (to cool the skin through evaporation) and our skin blood vessels widen (to
bring warm blood to the skin where it can cool).
"If we were feeling the warmth only when the ambient temperature reaches the same value as the deep body temperature, it would be
too late and hyperthermia would develop," says Ducharme.
The body temperature would soar and eventually cause brain damage.
(Answered by April Holladay, science correspondent, January 2, 2002)
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