"If normal body temperature is about 98 degrees Fahrenheit, why do we feel hot at that air temperature?"
—S. Meyer, Melbourne, Fla.
Jeffery W. Walker, a physiology professor at the University of Arizona, has a cool explanation:
The human body is like an engine that continuously generates large quantities of heat, and its radiator, so to speak, disperses heat least effectively in hotter climes.
Heat is an unavoidable by-product of the work being done by the tissues of the body. Contracting muscles of the heart, diaphragm and limbs; ion pumps that maintain the electrical properties of nerves; and biochemical reactions that break down food and synthesize new tissues (to name a few) generate body heat continuously. With this gurgling volcano of active internal organs, the body has a critical need to dissipate heat to the surroundings. It does so by circulating blood near the surface of the skin, by exhaling warm, humidified air, and by evaporating sweat.
These processes function best when ambient temperature is around 70 degrees Fahrenheit, where we feel most comfortable, and they serve to maintain core body temperature around 98 degrees F. But when the surroundings match core body temperature, the dispersal mechanisms are not optimal, so we feel hot, especially when humidity is high. Humidity has a significant effect because water on the body absorbs enormous amounts of heat and then dissipates it by evaporation. Anything that interferes with this vaporization of water (humid air, lack of a breeze, heavy clothing, and so on) makes us feel especially hot and uncomfortable.
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9 Comments
Add Commentthis is an interesting idea. Many people do not stop and think about these topics and discuss them further. The article was informative and well put together. That is an original discussion.
Reply | Report Abuse | Link to thisI wonder if this has something to do with why when I lived in Florida I found it hard to lose weight. Part of it was because I enjoy outdoor activities so much, but in Florida, it's just so hard to be outside during the day. Perhaps in a warmer climate our bodies just don't want to work harder.
Reply | Report Abuse | Link to thisreally i think it is the concept that if the temperature outside the body is low the body can get out of the heat that come from its own energy reaction so if the temp in air is like his own the H2O that come through his body will remain in side and the person feels hot " the concentration of heat transfers from high to low " so if its same at body and air body makes feed back to its temp. and starting to sweat to make heat difference .. as i think ..
Reply | Report Abuse | Link to thisI think the response is only part of the answer.
Reply | Report Abuse | Link to thissweat/water requires heat (the latent heat of evaporation of water/sweat) in order to evaporate. This it acquires from the skin making the body cooler and the skin feel cooler.
In high humidity where evaporation is limited/does not occur then sweating is not as effective so you feel hotter at the same air temperature.
(In fact the friend of a work colleague died as the result of the inability to sweat in high temperatures. He foolishly thought the lack of sweating was an asset and did not mention it until too late. (This was in a remote area)
Small note
Reply | Report Abuse | Link to thisTHe latent heat of vaporisation is the heat required to evaporate the water at a given temperature to water vapor at the same temperature. It is not the same as the heat absorbed by the water to get to that temperature
another small note
Reply | Report Abuse | Link to thisThe latent heat is why if you are sweating in a room you may feel hot. If you now place a fan in front of you, you will feel cool. This is not because of the cooler air from the fan,(its the same air at the same temperature), but that the fan is forcing the sweat to evaporate, thereby forcing the sweat to absorb the latent heat it requires in order to evaporate.
Dr Walker wrote that heat generating processes of the body function best at around 70 degree ambient temperature. Since much of the world's population functions just fine at much higher ambient temp. (at least much higher daytime ambient temps), I have to wonder about the evidence upon which he bases his statement. Personally, after living many years in the tropics, I (and the rest of the people here) manage to maintain functionality and body temp. just fine at much higher ambient temperature and humidity without excessive sweating and feelings of uncomfort. I think the body adapts to a wide range of ambient temperatures. In fact, 70 degrees feels quite chilly to me, and when I return to the SF Bay Area I invariably wear a sweater or coat at that temperature until my body readjusts. So, Dr. Walker, what is that "70 degrees ambient temperature" works best based on? In other words, I think comfort is relative to what one is accustomed to within quite a wide range of temperature and humidity.
Reply | Report Abuse | Link to thisSign me as "Doing just fine in the tropics!" :)
This is also why water at body temperature feels uncomfortably hot. I have discussed this in a blog post in relation to an inaccurate remark in a Jules Verne novel :
Reply | Report Abuse | Link to this<a href=" http://snailstales.blogspot.com/2005/08/dont-believe-jules-verne-on-hot-day.html">Here</a>
some people have not learned to feel "comfortable" with "wet perspiration" standing on their bodies (and especially the face)
Reply | Report Abuse | Link to thisthis ability is important in a warm humid environment
another tip: the simplest method to measure if one is sufficiently hydrated is to check on the "yellowness" of ones urine