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The Debunker: Is Human Body Temperature 98.6°?

by Ken Jennings

Lord Almighty, I feel my temperature rising. If you live in the Northern Hemisphere, July is the beginning of the “dog days” of summer, the hottest period of the year. But you know what’s cool on a hot day? Knowledge. Grab a tall glass of lemonade, settle down in a hammock under a shady tree, and let Jeopardy! wunderkind Ken Jennings set you straight on some shamefully persistent misinformation about hot stuff.

The Debunker: Is Human Body Temperature 98.6°?

My mom was a slave to the thermometer. A temperature of 98.6° meant that, even if I felt lousy, I was perfectly healthy and had to go to school. Anything higher meant a fever, so I could stay home and watch game shows and General Hospital. Anything lower meant I wasn’t holding the damn thing in my mouth right, and I got just one more chance before she’d go back to the medicine cabinet to get (ominous music sting!) the other thermometer.

hot blooded, check it and see

Sorry, moms: 98.6º isn’t actually a correct measurement of human body temperature. In fact, it’s an accident! The number dates back to 1868, when a German doctor named Carl Reinhold August Wunderlich took over one million (!) temperature measurements from the armpits of 25,000 different patients, and determined that the average reading was 37° Celsius. This translates to 98.6° on the Fahrenheit scale, a number that survived into the 21st century almost unquestioned. But there are two problems with this. First, the 37° Celsius measurement was accurate only to the degree, not to one tenth of a degree, so our “98.6°” should always have been “99°.” The .6 part is totally arbitrary. Even worse, nineteenth-century thermometers were footlong contraptions that took very imprecise measurements, and physicians looking at Wunderlich’s data today believe that his thermometers may have been calibrated as much as four Fahrenheit degrees too high! A 1992 study by the University of Maryland, using better technology, found that 98.2° is a more accurate population-wide average.

So does that mean Mom was right to freak out about a 99° temperature? Not so fast. Even Wunderlich wrote that a fever wasn’t “suspicious” until it rose above 38°C, which is why pediatricians sometimes still use 100.4°F as their cutoff. And the Maryland study in 1992 found wide variations in temperature based on subject, time of day, age, gender (men were slightly colder than women) and race (white subjects were slightly colder than black ones). In general, they concluded that the upper limit for a normal temperature was 98.9°F in the early morning and 99.9°F overall, but that’s just an average that may or may not be reliable for individuals. Ideally, doctors and parents know their patients well enough to tell a normal baseline temperature from a low or elevated one. It’s time to throw out the 1967 pop ballad by one-hit wonder Keith: 98.6, it’s not good to have you back again.

Quick Quiz: On what temperature scale does human body temperature measure a whopping 310 degrees?

Ken Jennings is the author of six books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at or on Twitter as @KenJennings.