# Is normal body temperature really 98.6 degrees?

(My apologies if this has been answered before – I could swear I’ve seen something about it somewhere, but I couldn’t find it in my searches.)

I remember being told once that body temperature is not really 98.6 degrees. The story goes like this: doctors (or scientists) calculated body temperature using the Celsius scale, and then rounded their answer off so that it would be an integer: 37 degrees. When somebody wanted to know the Fahrenheit equivalent, they precisely converted 37 Celsius to 98.6 Fahrehneit.

But if that Celsius temperature was rounded off, doesn’t 98.6 Fahrenheit have a problem with having too many significant digits? Does anyone know what the pre-rounding Celsius body temperature was? Or is this something my brain cooked up during a fever dream?

Thank you.

The latter.

The centigrade scale is determined by the melting point/freezing point of water (0) and the boiling point of water (100). It is a coincidence that the ‘normal’ body temperature appears to be a rounded number.

Are you sure about that, Dragon? I had heard that the temp was rounded to 37, and we just don’t know what the pre-rounding figure had been.

(In any case, I’m pretty sure that even if it was exactly 37 and didn’t need to be rounded, that 37 itself was merely the average temperature from a number of test subjects. “Normal” temp varies with each person, so no one should panic if their own if a little higher or lower.)

OK, I get the drift.

Now that we’ve brought up the subject, let’s talk a bit about human body temperature. Many clinical thermometers bought in the drugstore have a red line or an arrow at 98.6. There’s good reason, however, to believe that most well-fed, healthy folks have a modal temperature between 98 and 98.6. According to this interpretation, the hallowed 98.6 would be the high end of the range of normal, and 98.4 would be closer to a “normal” temperature. Supposedly the sacred number came about this way: nearly a hundred years ago there was a project to measure the body temperature of thousands of healthy people. The average came out to be 36.88 degrees Celsius (the scale was then called “centigrade”). The physician in charge sensibly rounded this to 37 ° C — and this is exactly 98.6 F. After that, every book on earth it seems trumpeted 37 or 98.6. However, go back about 100 years, before this survey, and it’s a different story: I have here in my hand Alfred Gage’s little book, Elements of Physics, published in Boston in 1889, and on page 152 it says, “Blood heat…98°.” Likewise the 1899 edition of Edwin Edser’s classic, Heat, reads “…the blood of a healthy man… 98° F.” And so on. Did you know that prior to 1866 you had to hold the thermometer in your mouth for 20 minutes to get a reading?

Here’s what I’ve always wondered: At what location in the body are they referring to when they say it is nominally 98.6 °F? I mean, your body is not in perfect thermal equilibrium, is it? Surely there are temperature gradients…

According to this webpage:

http://hypertextbook.com/facts/LenaWong.shtml

98.2 is closer to the average body temperature. However, a more useful statement is that 97.6 to 98.8 is a normal range of temperatures.

Every time I go to the doctor my temperature is in the 96 to 97 -degree range, and the doctor never comments on that. I always thought it was a little low. Been that way since I was a kid. But apparently there is quite a range of acceptable body temps.

My mother always taught me that 98.4 degrees F was “normal”. ski, where does the doctor take your temp from? I believe that under the tongue or armpit is usually a little cooler than, ahem, “internally”.

“Normal” body temp is normal for each individual. Body temperature is determined by your individual metabolism. someone with hypothyriodism will have a lower than average temp.
Therefore, 98.6F is an AVERAGE body temp.
Oh, and to answer the other question, with the advent of the electronic thermometers, the ear is most accurate. Lots of surface blood vessels.

I first learned that the 98.6 F figure is wrong due to roundoff error from reading John Allen Paulos’s book A Mathematician Reads the Newspaper. I see that the relevant paragraph from that book, or something very close to it, is quoted about halfway down this page (which is linked to on the page Wendell Wagner cited).

OK, here’s my situation. I’m quite hypothyroid; even with 2 thyroid meds and semi-annual endocrinologist exams, my temp averages around 96°. Fine - so I’m cold all the freakin’ time (except when it’s over 80°). I deal.

But when I feel ill and go to the doctor (my GP or urgent care center), the nurse takes my temp (by ear) and comes up with something like “98.8° - no fever.” No fever?! If a person whose average “normal” body temp is 98.6° has a nearly 3° rise in body temperature, they’d damn sure call that a fever, wouldn’t they? I mean, they know I’m hypothyroid if they look at my chart - but I suspect they don’t look.

All I’m sayin’ is, the average health care professional acts as if everyone’s “normal” temp is 98.6°, without even thinking about it.

Padmaraga - without thyroid trouble I have a very low normal temp, and a low resting heart rate, and low blood pressure. Everything is fine, I’m fine, it’s all fine – and doctors and nurses have never acted like this is remarkable. I suppose it’s just the luck of the doctor draw…