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Welcome to the Greenwood.Net Curiosity Corner

Core Temp

Aug 14, 2019

Curiosity Corner
Dr. Jerry D. Wilson,
Emeritus Professor of Physics
Lander University

Question: Our body temperature is 98.6 F, so why do we feel so hot at lower temperatures, such as 80-85 F? We perspire to cool our body, but at these temperatures, one would think the body would be cool enough. Also, if we jump in a pool or ocean with a temperature of 85 F, the body feels a chill before becoming adjusted. (Asked by Talmadge Luker, of Hodges, S.C.)

Reply: First, let’s take a look at how our body temperature is regulated—the balance between heat loss and heat gain. The hypothalamus, which is found in the brain, is the body’s thermostat. It regulates physiological changes that maintain the internal body temperature called the core temperature. This is around 98.6 F (or 34 C).

Not everyone’s “normal” body temperature is the same, however. The old “98.6” is just an average set by a German doctor in the 19th century, when thermostats weren’t exactly accurate. More recent studies put the body temperature of a healthy adult anywhere between 97 F and 99 F. Babies and children have a little higher range of 97.9 F and 100.4 F.

The hypothalamus regulates body temperature by various means. For example, when too hot, a dilation of the blood vessels in the skin is initiated. This carries warm blood from the core of the body to the skin, where heat is lost by radiation, conduction and evaporation. The latter results from sweating and evaporative cooling. When too cold, the constriction of blood vessels of the skin helps prevent heat loss. Shivering—the rhythmic contraction of muscles—produces heat. Also, muscles just below the skin contract, causing hairs to stand on end (with goose bumps at the base). This forms an insulating layer of air to keep us warm.

Now back to the question. Why do we feel hot when it is 80 F outside? Obviously, the body is not losing heat, probably because it is a hot, muggy day. The air temperature may be 80 F, but you have to consider the humidity. Taking temperature and humidity into account, the temperature we “feel” is given by the heat index. A temperature of 80 F and a relative humidity of 90% means the heat index is 113 F! Good enough for the hypothalamus to kick in and provide some cooling.

Jumping into a pool of 85-degree water and feeling a chill? This is well below the internal core temperature and one might expect a big chill. However, the skin temperature reacts first. Normal skin temperature depends on the air temperature and other factors, such as humidity. One average, it is about 91 F. So, a dunk at 85 F would make for a quick chill until the hypothalamus swings into action to warm you up a bit.

Hats off to the hypothalamus!

C.P.S. (Curious Postscript): “If the temperature is less than my age, I don’t get out of bed.” –Ellen DeGeneres

Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC 29649, or email jerry@curiosity-corner.net. Selected questions will appear in the Curiosity Corner. For Curiosity Corner background, go to www.curiosity-corner.net.

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