Why is 98.6 just right for your body but too hot for the weather?

Slate has a nice explainer covering heat wave health problems. The central question: If my body temperature is 98.6 degrees Fahrenheit, why am I uncomfortable when it's 98.6 degrees Fahrenheit outdoors?

The answer is both basic and interesting. Sure, 98.6 degrees F is the healthy temperature for a human body, but that's only because we are pretty good at transferring heat away from ourselves. Your metabolism and your muscles generate more heat than that, but you get rid of it using tricks like breathing out hot air and sweating. Basically, your body works like a heat exchanger. It's the same sort of system that keeps your refrigerator cool—take the heat from inside a closed space and dump it into the surrounding environment.

Unfortunately, this system works best when the surrounding environment is cooler than the closed space. Your body is happiest when the air temperature is around 70 degrees F. That's when it's most efficient at getting rid of your excess heat. When the weather gets to warm, it's a lot hard to make the heat exchange. With nowhere else to put the heat, your body temperature starts rising.

Because exercise causes the body to generate so much extra heat, optimal temperatures for intense physical activity are lower than those for daily life. Athletes can raise their core temperatures six degrees just by working out. Add an environment that makes heat dispersal more difficult—not to mention possible dehydration from sweat losses that sometimes exceed six liters (for marathoners) or two liters per hour (team game players)—and performance can take a nosedive.

... For example, researchers in Darwin, Australia, observing a long-distance runner taking a 30-minute jog through the humid air, noted that his body temperature increased from 98.96 degrees to 105.8 degrees. When he’d gone on a similar jaunt under cooler conditions, his temperature had risen by just two degrees. Such a spike spells trouble for maintaining an optimal heart rate: The man’s soared to 200 beats per minute during the last 15 minutes of his run, where, previously, it was a more sustainable 154 beats per minute.

Read the rest of Slate's Explainer on body temperature.

Image: Suck It Heat Wave!, a Creative Commons Attribution Share-Alike (2.0) image from instantvantage's photostream


  1. Your body is happiest when the air temperature is around 70 degrees F.

    Below 85° and I’m shivering.

    1.  Speaking for the warm-blooded species here, somewhere around 17-20 degC is good for me.

    2. I have the oppostie problem.  Above 75 and I’m sweating.  I’m happy around 50 and sunny or 60 and cloudy or breezey.

      (You’d never surive my house during the winter 56 is the best I can afford.)

      1. I used to be almost exactly the same way, but then I moved to SoCal from Buffalo. I still sweat easily when it’s really hot, when everybody else is sweating too, but I adapted fairly quickly to normal California temperatures (even out in the desert). And now back in Buffalo, I am much less tolerant of cold.

        I think most people will tell you that there’s an optimal climate for them, but in reality most people can adapt, to some degree, given enough time. 

        Of course your body type plays into it as well, but not as much as I thought it would… I’m kind of stocky and occasionally slightly flabby and that wasn’t a big issue in California and didn’t protect me from the cold in Buffalo after adapting to CA.

        1.  I think most people will tell you that there’s an optimal climate for them, but in reality most people can adapt, to some degree, given enough time.
          I have yet to adapt to Baltimore summers and I grew up here.

          1. Yeah… a lot of people from elsewhere in the country don’t really understand how terrible summers in east coast states can be, even in non-heatwave years. The past few weeks in Buffalo it’s been as bad as Thailand in the hot season.

  2. Heard some time ago that the temperature that the naked body feels neither hot nor cold is 81 degrees.

    1. My baseline body temperature runs between 95.5° and 96.5°. It certainly seems to affect my need for warmth.

  3. Someone proofing this stuff?

    “When the weather gets to warm, it’s a lot hard to make the heat exchange.”

    Should be:
    “When the weather gets *too* warm, it’s a lot *harder* to make the heat exchange.

  4. Can we get a browser plugin that automatically converts silly scales of measurement to sensible ones?

    Ill have my temperatures in °Rø please.

  5. Only cowardly prudish people think 98.6 degrees is the body’s natural body temperature.

    All assholes know that it is higher than that…

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