Calor. Or: The myth of 98.6° F?

Ever wonder how it was determined that 98.6° F is the “normal” human body temperature? Ever wonder how that number was determined and how accurate it is?

The Inveterate Persiflager explains.

Not surprisingly, it turns out that “normal” body temperature is more variable and less clear-cut than is commonly thought.


  1. #1 Joe
    September 29, 2008

    Hey, 98.6 it’s good to have you back again …

    I hope the Pesiflager looks here, because there is a typo in the post. “The mean temperature varies during the day, lowest at 6 AM (37.2°C (98.9°F))” If the average temp. is 98.2°F, as is repeatedly claimed, the lowest temp. cannot be 98.9°F.

    I could not be bothered to set-up a login at that site.

  2. #2 kassiane
    September 29, 2008

    that’s kind of awesome.

    At 96.5 degrees and female mid afternoon, I still run ridiculously cold.

  3. #3 Martin
    September 29, 2008

    There is more to the story than that. In the UK I grew up learning that the normal temperature (blood heat as it was marked on my grandfather’s hot-house thermometer) was 98.4°F. I suddenly noticed US medical dramas on TV like St Elsewhere and ER where people talked about 98.6°F and never knew why. It was years later that I realised it was just a straight translation of 37°C.

    My understanding was that Fahrenheit intended blood heat to be 100°F and used his own temperature to measure it, but unfortunately he had a bit of a fever that day.

  4. #4 Barbara
    September 29, 2008

    This is just great! Stripping away at the comforting standards of life leaves us feeling lost! How can the all time determinant of illness – abnormal temperature be spurious?!

    Next thing you will be telling us that discussing our fears with a physican while reclined does not improve mental health! Worse! – Don’t even think about suggesting that a natural and eventual adaptation didn’t transition hominids to modern humans. That would change world order!

  5. #5 Ancient Brit
    September 29, 2008

    My wife has a “normal” range of oral temperature of between 94.6F and 96.4F, so whenever she visits our GP and the measurement is around 99F, we have the devil’s own job to convince the nursing assistant that this is not “normal”.

    Years ago in the UK such departures from the norm would be marked clearly on the front of the folder containing the patient’s medical notes, to give the nurse (or GP) a heads-up.

    For some reason in the US there is incredible resistance to such practice (in 13 years of marriage and residence in SoCal I have never been able to persuade any doctor or nurse that this low normal range is something that ought to be flagged).

    It means that every visit we make to the GP (or indeed any medical services provider) has to be a joint effort. One voice explaining that 99F is not to be ignored seems to get nowhere – it definitely takes two.

    One experience with a prior GP that sticks in my mind is a period of three weeks in which my wife’s temperature didn’t drop below 99F, coupled with a dry hacking cough triggered every few minutes, even during sleep. Several visits to the HMO GP elicited no concern at all – the suggestion was made that my wife should suck a Halls mentholyptus cough drop for relief.

    Finally in exasperation I insisted to the point of rudeness that the GP should do more, since there was clearly something going on. The lady very reluctantly wrote out an X-ray request, and when we returned with the films, her only comment was: “Oh, look, your wife has ambulatory pneumonia. I guess I’d better prescribe some antibiotics…”

  6. #6 DLC
    September 30, 2008

    The Fahrenheit system was invented about 20 years before Celsius, so I doubt it was an issue of the Fahrenheit system being faultily calculated. probably more a matter of a difference of opinion about body temperature.

  7. #7 Natalie
    September 30, 2008

    My wife has a “normal” range of oral temperature of between 94.6F and 96.4F, so whenever she visits our GP and the measurement is around 99F, we have the devil’s own job to convince the nursing assistant that this is not “normal”.

    It’s even harder as a child. I’ve run cold my entire life, and I distinctly remember arguing with a school nurse once about the fact that I had a fever. When she took my temperature it was about 1 degree higher than “normal”, so she reluctantly let me go home. But she told my mother that she thought I was making a big deal out of nothing.

  8. #8 tony
    September 30, 2008

    I also generally have a cooler body temperature (around 36 Celcius), have a slower heartrate (less than 60 bpm resting), breathe more slowly, and I’m also more immune to external temperature fluctuation (from walking across a bitterly cold north-east parking lot in my shirt sleeves, to walking across a blisteringly hot and humid southern parking lot in a jacket and tie).

    Maybe my greencard has it right, and I’m *really* an alien.


  9. #9 The Perky Skeptic
    September 30, 2008

    Boy oh boy, I know whereof you speak, Ancient Brit! I run cold, too, and when my temperature reaches 99 degrees F, something is seriously wrong with me. Also, I seem to have a harder time breaking a fever than those who run hotter.

  10. #10 usagi
    September 30, 2008

    Nice to know there are so many other cool runners out there. It does sometimes feel odd explaining, “No, I may still be under a hundred, but that’s 3 degrees above normal for me. Really. Something’s off.”

  11. #11 Samantha Vimes
    October 1, 2008

    The thermometer usually reads around 97.4 when I’m feeling well. And yes, I thought my fevers didn’t measure as high as they felt strongly enough that I *did* work out– I vary from 97.2-98.4 comfortably. At 99 degrees, I know it’s more than normal variation!

    …. and it’s *nice* to know this is not so unusual.

  12. #12 Samantha Vimes
    October 1, 2008

    Okay, off-the-cuff survey: how do cool runners react to external temperatures?
    tony doesn’t mind heat or cold.
    I’ve never encountered cold temperatures I couldn’t put up with for a good while without extra layers, but an external temperature above 75 F makes me uncomfortable (heat triggered asthma, though, being largely to blame for it). It’s like my body needs the cooler body temp and does manufacture a lot of heat but needs a cool environment to disperse it.

  13. #13 Natalie
    October 1, 2008

    See, I’m the exact opposite. I hate cold and I seem to feel colder than other people do. Heat doesn’t really bother me.

  14. #14 Ancient Brit
    October 1, 2008

    Okay, off-the-cuff survey: how do cool runners react to external temperatures?

    My wife generally prefers lower ambient temperatures (anything above 72F is considered unpleasantly warm), but she also suffers from lifelong super-obesity (which may be a function of the chemistry resulting from the lower body temperature), which may be a factor.

    Baryatric surgery over the last several years has reduced the severity of (but not eliminated yet) the super-obesity, but she has still maintained the same ambient temperature preference.

    (I have a pet theory – completely unsubstantiated – that clinical obesity can be divided into many different subtypes, one of which may be the result of abnormally low body temperature – possibly the result of unrecognised mitochondrial malfunction, perhaps caused by viral or other infection.)

  15. #15 themadlolscientist, FCD
    October 1, 2008

    I run cool too – typically around 97.2F – and I don’t tolerate cool temps very well. My comfort range is around 78. If I’m sitting still for any length of time and the room temperature goes below about 75, I can start to feel cold. Below about 72 you’re likely to see me in a hoodie, wearing gloves with the ends of the fingers cut out. OTOH, “too warm” doesn’t kick in much below 85 as long as it isn’t humid.

  16. #16 Aquaria
    October 1, 2008

    Another cool cat here. I typically run 97, and have gone round and round and round with doctors that I am seriously ill when the thermo says 99 or above. This wasn’t a problem when I lived at home; my mother was a CRNA, we always ended up going to doctors she knew well, and they would listen to her when she’d tell them, “This kid runs low. Really low. 99 is well over 100 for her. She’s been 100.2 to 101 for X hours, with symptoms ABC. We’d better run some tests.”

    But that changed when I left home. It’s like I became a moron and a liar. I’d love to not have to be in a doctor’s office every week for a while, then every few days for a while longer, requiring more dire treatments for ailments that could have been alleviated much more quickly and with gentler treatments if only the doctor would have just listened to me! I’m not making up having a low temp. The only reason he would have this long list of 99.2 temps is because I keep having to go back to him because he didn’t listen to me when I said I run low, and didn’t treat what was wrong with me when I was at a mere 98.3! Even changing doctors does not fix this very bad habit American doctors have of “98.6 fits all”; finding a new MD only means I have to start over!

  17. #17 Aquaria
    October 1, 2008

    I’m one of the cool cats who can’t stand heat. In normal years, I ditch the shorts for trousers only if it gets below 40, which doesn’t happen often in San Antonio. If I want to change up my wardrobe, I might wear some Capri pants. But that’s not for weather. Just a change of pace. And sometimes I actually blow the dust off a dress or skirt. But you can bet there’s not one wool or cord piece in the bunch. It’s all cotton, silk, and other lightweight fabrics. And forget stockings. I haven’t worn a pair since…



    I think Clinton was President the last time I wore those awful things! Yep, I don’t wear them because they’re TOO HOT.

  18. #18 Samantha Vimes
    October 2, 2008

    Oh, yes, Aquaria. Trying to get doctors to believe about quirks that make us non-standard… I also have White-coat Hypertension and my asthma is mostly masked by the fact I used to run long distances AND play saxophone, so I have enough experience in controlling my breath to force air through almost any condition. Mind you, I’ve dislocated a rib at times, trying to breathe.

    I like m y new doctor, because she talked to me longer than most of them, and listened… and I could see the mild skepticism change as she heard me using technical terms and talking about how I try to minimize use of medications, etc. By the end of our meeting, I think we were both very comfortable with each other.

  19. #19 Arrow
    October 2, 2008

    First of all, congratulations on a great blog! Coming here to read RI a few times a week is such a welcome relief. I am originally from Hungary, but spent 17 years in the US and Canada as a research scientist (vascular biology).

    Right now I am living in Hungary once again and it is a highly woo-infested area. I am currently unable to convince my mom that a story about someone who had cured her diabetes by using a mixture of herbs published in Blikk (local equivalent of some of the less restrained US tabloids) is not totally believable. Also she claims that she heard that the composer Puccini had cured his diabetes by living on coffee and cigarettes. My brain hurts.

    About temparatures: I grew up in Hungary with the rule of thumb that healthy body temperature was around 97.9 F. Above 98.6 F they called it an elevated temperature, and above 99.5 a fever. Having a normal body temperature of about 97.2, I usually start feeling sick right around 98.6, and have never had higher than 101.3 F. So yeah, I have had my share of having to explain again and again about my body temperature.

    On the other hand, I am almost never cold. Spent three years in Calgary where it goes down to -27 F or so every winter, and never had any problems. In fact, I have bilateral hip osteoarthrosis so I kind of gave up wearing socks at some point and I was fine in Calgary.

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