147 comments

[ 3.4 ms ] story [ 98.3 ms ] thread
They didn’t directly mention it in the article, but I wonder about increases in sedentary lifestyles over that same time period. Base metabolic rate would go down as an average as sedentary lifestyles increase.
As the article says, Wunderlich reached a conclusion of 37C in the 1800s, and that’s what we’ve used since then.

The real problem appears to be that converting to Fahrenheit and reporting this as “98.6F” suggests an order of magnitude more precision than “37C”. 36.5C would still round to 37 but corresponds to 97.7F.

I thought the same, so I tried to find Wunderlich. The only source I could find (https://www.google.com/books/edition/_/3-wHAAAAIAAJ?hl=en&gb...) seems to have Wunderlich reporting "98.6F", and then converting to Celsius:

> The average normal temperature of the healthy human body in its interior, or in carefully covered situations on its surface, varies, according to the plan of measurement from 98.6° to 99.5° Fahr. (37° to 37.5° C.). It is about 98.6° in the well-closed axilla, and a few tenths of a degree higher (.5-1½ or 2° Fahr., .7° Fahr. average) in the rectum and vagina.

So, as far as I can tell it's not a sig-figs issue in conversion, but the actual original source that produced "98.6°". It almost seems like Wunderlich should've used 37.0° to 37.5°C to be consistent.

That is a translation artifact. The German original cites 37-37.5 degrees Celsius on average: https://archive.org/details/dasverhaltender00wundgoog/page/n...
(comment deleted)
Gah! Of course Wunderlich didn't write the original in English, and I should've looked for the original in German.

I'm a little surprised and disappointed that the translation also translates the units, though. That seems to be stepping just outside the bounds of what I would want translated (at least, in the context of a medical journal or scientific writing).

Thanks for that correction!

Interesting that the original german text uses Celsius as the primary measurement, and provides conversions in Rankine. No mention of Fahrenheit.

Funny that people argue over this and some guy named Wunderlich who measured a bunch of asses.

Did he write that translation or is Google Books fake news?

It's obviously not rankine, seeing as it gives a conversion of ~30R = ~40C. Looks like its actually Reaumur: https://en.m.wikipedia.org/wiki/R%C3%A9aumur_scale
Well the more you learn, thanks.

Actually makes it even more interesting, Wunderlich and his reaming to get some Reaumurs.

What were his actual measurements taken in and how accurate was his thermometer? And who's vaginas has it been in?

Curious I get flagged for pointing out the potential measurement inaccuracies and the errs of scientific reproducibility, all while having some humor.

I have always been taught that 37C is the upper limit, actually bordering on fever. So 36.5C or even a bit lower was always considered healthy and fine.
Same here, 36-37 normal, over 37 fever.
Same here, but I've since readjusted :)

Currently the top comment says "Basically, in our experience, anything below 38.4 °C could just as well be caused by any of a number of non-fever conditions at something like a 90 % confidence level" ... which is panicky territory for me. But anything under 38 is fine.

Well, if I have anything above 37.5C, I definitely feel ill. If you call that fever, or something else, feels hypocritical to me. Luckily, this stuff is a continuum. Still remember the 40.6C as a child, as my sense of equilibrium completely went bonkers and I start to hallucinate.
I was brought up with everything under 38 being subfebrile (Dutch "verhoging") which means to watch out, but no need to call the doctor yet.
I wouldn't call a doctor as long as I am below 40C, but thats maybe just me not wanting to uselessly overload the system... Other people seem to have different attitudes. Come to think of it, our local media just had an article saying doctors are asking patients to not come to the doctors office just because they have a little fever. A similar thing seems to happen in children ambulances. Doctors tell me that 90% of the cases there are just clogging the system and making it harder to find the 10% which really need immediate help.
I never let it hit that high. I take something. By the time I hit 39.4, I'm at the point that I'm nearly hallucinating. I can't stay sitting upright in a doctor's office and simply cannot drive myself. I wouldn't trust myself not to get lost walking 2 blocks to the hospital.

I've had this happen as an adult: The doctors office had me take 800mg of children's ibuprofen and had me wait until the fever started coming down: If it didn't, they were going to call an ambulance. Sidenote: Children's liquid medicine tastes horrible.

40C (104F) isn't just a little fever, and is definitely in the danger zone for both children and adults. You should probably get to the doctor before that, in general - especially if you react as I do at a lower temperature.

You don't have to call the doctor when you hit 38, but I would definitely do that before you hit 39.
I've been taught [37,38) is raised temperature/light fever and >=38 is a serious fever.
Not sure if it's all the countries, but I have always heard the normal body temperature in Celsius stated as 36.5, which is 97.7 F.

Is 98.6 an american-only thing?

In my country is more like: Normally you should be 36.x; 37 would be a little bit high but not yet fever.

I personally think it really isn't that important though, because how people measure it is way more imprecise/fluctuant than the standard itself.

We (Australia) have always in my experience taught and been taught a range.

eg:

> You probably have a fever if your temperature is 38°C or higher.

> A normal temperature is around 36-37°C, although it depends on your age, what you’ve been doing, the time of day and how you take the measurement.

( further notes on taking temp., children, etc. )

https://www.healthdirect.gov.au/fever

Yes, it's a conversion of 37C which is stupid since 37C is when I have a fever already
37 may or may not be a fever depending on your activity. If you went running your body temperature will be above 37 but you'll feel perfectly normal. When you got 37 and it's a fever it feels different.
Knowing that my resting body temp was permanently 36.8-36.9 while everyone elses (on the same thermometer) was 36.6 was one of the things that led me realise something was wrong and in fact it turned out I had an autoimmune. Of course the temperature fluctuates with activity and with the time of the day but an auxiliary reading of 36.6 has been what I've always observed for myself and others. After all we all run the same biochemical processes that are optimal at this temp.

As a side note, I hate digital contact thermometers with passion. Mercury is dangerous as hell but if it wasn't for gallium alloy ones I'd smuggle them in the country.

>Mercury is dangerous as hell but if it wasn't for gallium alloy ones I'd smuggle them in the country.

It's elemental mercury encapsulated in glass not one of the organic compounds that cause all the acute and longterm health issues. Chlorine bleach is scarier stuff used in the household.

The thing about mercury is that it accumulates, but chlorine does not.

Mercury is mostly banned for being persistent pollutant, next after lead. There is no real safe level of mercury intake due to cumulative damage and hard for body to get rid of.

There is a safe, heck, required level of chlorine intake. (What is table salt?)

Mercury is not any superior at measuring temperature over a resistive electronic or a bimetallic thermometer, or alcohol capillary one. (Except the latter boils and freezes too easily, not a problem for body temperature.)

Although in theory electronic thermometers can be just as accurate in practice I've found that across brands the measurements fluctuate to an unacceptable degree.
What should we know about bleach?
For one, not to mix it with vinegar. Chlorine gas.

There was a spate of TikTok's recommending mixing them for cleaning purposes. To the horror of many.

Drink elemental mercury and you'll be fine, it'll just pass through and you'll shit it out.

Drink bleach and it'll probably kill you or at least give you terrible injuries.

Ok, guess I should have asked, what should we know about bleach besides the warnings prominently printed on the bottle. Tbf I really don't expect everything in my house to be edible.
My thermometer is a cook's infrared no-contact instant-read thermometer (I also own a digital under-tongue thermometer, but I no longer use it). The cook's thermometer is more accurate.
Obviously, I'm talking about waking temperature, if I wake up at 37C I have a fever since my normal is 36.5-36.6
50 years ago, I was taught 36.6C is normal. The thermometers we used, back then, had a mark at 36.6C.
Brit here; I was taught that 98.4F is "normal". Clearly I'm abnormal; my own temp is nearly always higher.
We've been using 98.6F as the threshold for fever in India for as long as I can remember (I'm 40 years old) even though for everything else we use the Celsius scale.
As an American, I can’t say if it is American only. I can say 98.6°F is the commonly accepted healthy body temp.

I have noticed over the last decade, nurses checking my temp are more likely to say something like “You are 97.6°F. That’s normal.”

I have always felt that 37C was way too precise an answer for a human's body temperature. How is it that a measurement based on the freezing and boiling point for water coincidentally lands on a nice even number for a human's body temperature.

It's one of my issues with biological sciences that they sometimes try to come up with precise answers as they do in physics or chemistry, when most of the time answers, such as this, should be phrased as "around 37C" instead of "it's 37C".

Even “around” is meaningless without context. A hot day is around 37c (+/- 10), a healthy person is around 37c (+/- 1) and a manufacturing process could call for a temp around 37c (+/- 0.1).
The accuracy is implied in the nimber of dogots usually.

So 37 is +-1C, 40 is +-10, and 36.6 is +-0.1

Doesn’t work great when you want high precision on a number that ends with zeros or have a range that’s not a multiple of ten.

The real answer is standard deviation or something like that.

Sure it does. 10000 and 10000.000 have vastly different precision.
10,000 doesn’t disambiguate between an error of 1, 10, 100 or 1000.
1e4 does though (vs. 1.0e4, 1.00e4, etc.).
Scientific notation is the answer to this problem.

3.00 * 10^3

versus

3 * 10^3

The accuracy being implied in the “nimber” might not be intentional but it’s a great demonstration of the principle.
I was googling 'nimber' and 'dogot' because I thought it was some obscure but extremely relevant concept that I didn't know about.
The obscure, but extremely relevant concept is the English QWERTY keyboard layout, which places U, I, and O next to each other and makes typos like this more likely when you touch-type with two hands :)
>The accuracy is implied in the number of digits usually. >So 37 is +-1C

Yeah, but this doesn't work for human bodies when you round 36.5 either up to 37 or down to 36.

* 38C is surely fever, 37 is mild fever for most people;

* 36C is below-normal for most people, and 35C is surely hypothermia.

36.5 - 37C is the normal temperature range.

Would 45C be ±1 or ±10?

You can't provide a scaled ranges with the digits alone like that.

Just use ± or a hyphenated range, and take it in context with adjacent measurements.

> A hot day is around 37c (+/- 10)

Absolutely not. 47C is an emergency, not "hot".

Ah, memories of quiet summer days in Western Australia! No emergencies as far as the eye can see. The wind feels like a hair dryer in the face. Ah yes, a summer day in the sticks.
You know, there might be a reason the population density in Western Australia is reportedly 1 person per square kilometer.

Or as Population Australia put it:

> The state’s capital city is Perth. Perth has an estimated population of over 2.7 million people.

> Western Australia is Australia’s largest state. Its total area is 2,529,875 km² which accounts for 33 percent of Australia’s total land mass.

> Based on our research Western Australia population will reach 2.879 million by the end of June of 2023.

Most of Western Australia, of course, is not Perth. The density outside of Perth is... 0.2 people per square kilometer, using poorly-defined and chronologically mismatched statistics from the wikipedia sidebars. Perth has 80%+ of the people of Western Australia in 0.24% of the space. If we believe Population Australia about the size of Perth, it has more than 97% of the population of Western Australia in 0.3% of the space.

I feel strangely comfortable characterizing temperatures that prevent humans from living in a region as "emergency" temperatures.

The population density of Sydney is 2037 people per square KM according to Wikipedia, it's not uncommon to get days with a temperature of 35-40 degrees and we aren't dropping like flies either.

I quite like a nice warm day.

Humans live in warmer climates than that and have done since before the invention of air conditioning.

You might feel uncomfortable if you're not used to it but you're not going to die if you stay hydrated

Maybe you're thinking of wet bulb temperature?
In Poland normal has always been considered 36.6C, which is 97.9F, which the article states as a proposed new normal.
Same in Russia, Ukraine, and other former USSR countries AFAIK
37 degrees (98.6 F) could already get you off school if you're lucky...
36.9 with a sad face would do.. I mean mercury is past 9 mark so it's pretty much 37, right?
Being friends with the household cat was very important for such strategies ;)
Graphite is tasty though
To add, < 38°C (100.4°F) is not considered a fever but subfebrile.
Sometimes I feel more sick having 37.5° than 38°, I don't know why.
Body temperature can be increased by several factors other than defense mechanism - cardio exercise and other activities that raise body's metabolic rate.
Possibly because your 37.5 is from your body trying to reach 38 but not getting there yet. I'm just recovering from influenza right now and over the past two weeks I've noticed that pattern very clearly -- I feel worse when my temperature is 37.5 and rising than I do when my temperature is 39 and steady.
Same in Italy.

36-36.6 is considered normal, 37 is considered a mild alteration (or life threatening disease if you're a man).

that's for a very specific reason: improved accuracy.

Let me explain: measurements were usually taken externally from armpits, using analog mercury thermometers, which results in temperatures lower than the actual one by ~0.5 degrees Celsius.

If you read the instruction manual of modern digital thermometers, that are more accurate, it states that

  Oral
  Time: ~55 seconds
  Typical temperature interval: 35,5~37,5 °C

  Anal
  Time: ~45 seconds
  Typical temperature interval: 36,6~38 °C

  Armpit
  Time: ~70 seconds
  Typical temperature interval: 34,7~37,3 °C
An example (PDF / Italian)

https://www.doctorpoint.it/images/deplian/docp-pdf10956.pdf

The science has always been sound, even in Italy.

My parents worked in healthcare, I never had the chance to skip school unless the thermometers said > 37.5 °C and after a double check with both palms on my forehead because I warmed it more than once on the radiator.

The problem is Italian paranoid moms, especially from the South, believing in spooky superstitions.

Personally I strongly doubt that "modern" thermometers are in practice more accurate than good ol' mercury ones.

The contactless infrared ones, but also the contact digital ones have been proved to provide "false measurements", the stated accuracy is usually +/- 0.2 C, but there are many (ambient) factors that may influence greatly the result, the good thing being that they are very fast.

The gallium/galistan ones (1:1 replacement for mercury ones) are often hard to read (they are almost all of the "prismatic" kind) and more often than not they simply get "stuck", and they are very, very, slow.

> Personally I strongly doubt that "modern" thermometers are in practice more accurate than good ol' mercury ones.

they are not more accurate per se, the reading and calibration is.

many cheap thermometer were printed with the temperature lines out of scale or shifted.

they are also safer to use, it wasn't uncommon that the old ones broke while using them.

Imagine the danger of a glass tube filled with mercury breaking while measuring the temperature anally or from the mouth.

>they are also safer to use, it wasn't uncommon that the old ones broke while using them.

>Imagine the danger of a glass tube filled with mercury breaking while measuring the temperature anally or from the mouth.

Oww, comeon, they are of course safer, but it is not like "it wasn't uncommon".

It was (and is for the - still largely glass made - gallium ones) an extremely rare occurence that a termometer broke while in use, though they often broke when they fell accidentally and - at least according to EPA - that seems like a serious hazard:

https://www.epa.gov/mercury/what-do-if-mercury-thermometer-b...

I cannot find any statistics on actual cases, but judging from this article preview:

https://www.sciencedirect.com/science/article/abs/pii/S02782...

they counted at the time 43 cases of mercury poisoning of which 7 related to broken thermometers while in use, and of these 7, only 1 was about thermometer broken while in the mouth affecting the oral mucosa.

The reported "new" one was about a lady that had her cat striking her in the face while she was using the thermometer in her mouth.

Please consider the fact that the World is larger than the USA and that we were talking about Italy and specifically I was talking about thermometers breaking in hospitals in Italy - a work place I've been acquainted with for 4 decades -, not about lead poisoning.

Please also consider the fact that Italy is in the EU, EU made those kinds of thermometers illegal in the Union with the directive 2007/51/EC [1] that was ratified in Italy by the decree n. 245 on 18.10.2008 which basically made it illegal to sell measuring instruments containing mercury since April 3rd 2009. Mercury is considered toxic waste in EU.

[1] https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex%3A...

I don't get it.

Surely they were made illegal by the EU directive and the following Italian decree.

That doesn't mean that people in Italian hospitals having thermometers break in the mouth (or other orifices) was "not uncommon" (possibly we use different definitions for not uncommon).

Unless - of course - you can recall many cases in your 40 years of acquaintenance with hospitals in Italy.

Let's say that a hospital has 100 beds and average stay is one week, that should be in the ballpark of at least 52x100x2 (temperature checks) = 10,000 measurements per year x 40 years around 400,000 uses of thermometers (possibly many more).

How many of these accidents can you remember roughly (1, 10, 100, 1000)?

> That doesn't mean that people in Italian hospitals having thermometers break in the mouth (or other orifices) was "not uncommon"

As I've said, I'm familiar with the specificity of Italian hospitals, and I'm saying to you it was not uncommon.

Does not mean very often, it means "something every person working in healthcare has been trained for, because it happens (happened) more often than you might think".

Especially if you think about the fact that I've already specified that they simply broke, not that "they broke in people's mouth" all the times.

> Let's say that a hospital has 100 beds and average stay is one week

Let's say that the average Italian hospital in big cities has hundreds of beds, at the times of the ban on mercury Rome had ~6 beds every 1,000 residents, US had 2.7 of them.

Let's also add that in Italian hospitals you don't pay for the bed.

My mom stayed in hospital for 6 months when she had tuberculosis.

Many of the patients in the same ward staid on average for a year.

> 10,000 measurements per year

That's per week here, probably more than that.

The hospital where my parents worked has > 1 thousand beds and > 5 thousands employees.

Not counting the ER and daily scheduled examinations.

And it's not the biggest one.

>That's per week here, probably more than that.

Good, so in a week, or 10,000 thermometers uses, how many broke, on average?

1, 10 or 100?

And we are talking only of those that you prompted to imagine the danger of:

>Imagine the danger of a glass tube filled with mercury breaking while measuring the temperature anally or from the mouth.

As for being a man - I think there was research that showed that men indeed have it worse during common cold :)

Also, I was one of the men that complained a ton during cold. Turned out, at the age of 34, that I had a deviated septum and the level of nose congestion when I was healthy was comparable to when I was healthy. Even slight cold was absurdly doffucult for me. Since they fixed it, the colds are super light for me.

But I had to take my girlfriends’ laughs for 8 years each time I had cold.

I never miss an opportunity to mention this story when people laugh about some people having „man colds”.

Wow. I am from the US. I have never heard of a man’s cold or that men suffer greater cold symptoms. Is this a commonly known thing where you are from? It sounds like you have a specific expression for it in your language.

What country/ language, if you don’t mind me asking?

In Japan, a lot of people think that 36C is the norm. In South Korea, everyone thinks it has to be 36.5C. Either the average swings quite widely depending on your ethnicity and/or environment, or everyone is confused about how to round floating point numbers.
"In Wunderlich’s day, tuberculosis, syphilis, chronic gum disease, and other inflammatory conditions that can raise body temperature were common"

That part resonates with me. I had a pretty bad tooth infection after delaying seeing a dentist for a cavity. (which is a mistake I will not make again), and during the few months I had a body temp probably a degree celsius higher than usual.

Given the state of dental health over 150 years ago and that a lot of data came from soldiers there may just have been a lot of inflammation going on.

As someone who has always been 96.5/35.8 - I will say that having a higher body temperature being the standard works out well when you come running in flushed to your check-in gate at the airport, and they take your body temperature (Covid thing) - and you still come in well under the acceptable range.
During the pandemic, some shopping centers in my area started to measure wrist temperatures. Once, my wrist was still cold from winter temperatures outside:

"28.5, ok, next"

> During the pandemic, some shopping centers in my area started to measure wrist temperatures.

They were supposed to measure your forehead temperature with that infrared thermometer. But due to some insane rumor spread around the net about these thermometers somehow hurting the pineal gland or something like that, everyone starting measuring on the wrist, even though it's way less accurate.

It was always completely pointless pandemic theater regardless of the measurement technique.
I thought use your palm is sort of ok.
Oh cool, I don’t just run cool, everyone does. Cool cool cool.
I was glad to read this, I’ve thought every thermometer I’ve ever had was inaccurate when I get readings like 97.5 all the time…
Normal body temperature seems to be falling over time. An analysis of 20 studies between 1935 and 1999 found that the average oral temperature was 97.5˚ F. And a 2017 study of more than 35,000 people found an average body temperature of 97.9˚ F.

I wonder if this can explain rising worldwide rates of obesity.

It's mentioned in the article that being overwhere is a potential explanation. Hard work surely increases your body temperature.
Several people in the medical field have told me they do not consider 99.x as a fever.

Edit: Found a link:

https://www.osfhealthcare.org/blog/whats-considered-a-fever-...

100.4 is their threshold.

As a dad, I don't consider my kids to have a fever until they are closing in on 101. They each run hot to begin with, but also the thermometers generally available to the public never seem to be particularly accurate.
> [One key possibility] ... Lower metabolic rate: One of the biggest determinants of body temperature is your metabolic rate. Like a car engine that’s idling, your body expends energy just keeping things going, and that generates heat. A lower metabolic rate in modern times could be due to higher body mass (some studies link this with lower metabolic rate), or better medical treatments, preventive measures, and overall health.

I know it's not exactly "thinking with statistics", but it strikes me as too coincidental that the obesity epidemic has only exploded in recent decades too.

It seems very likely to be metabolic rate. Most people are way more sedentary than in the past.

I'm curious how direct it is. If someone starts exercising from being sedentary for years does their body temperature raise appreciably?

I wouldn’t be that surprised to hear that they were always running slight fevers, though. The past was disgusting.
It makes sense. I think it explains some of it.
This is what I came to say. When I was a teen my body ran hot, so hot people used to even comment at times it felt like I had heat coming off me. My normal temps were in the low 99.

Now, as an adult, my metabolism nosedived. I barely feel like eating once a day. It's not abnormal to get temps in the 96s, though that could just be the cheap covid thermometers.

I'm in my late 40s, people around me still comment that I'm radiating heat (and have commented that for at least 30 years), and I almost always feel too hot - used to walk with a short sleeve shirt in the dead of snowy winter when I lived in NYC.

But my temperature when measured is consistently below 36 celsius, often 35.

That’s an interesting idea, although overweight people actually have faster metabolisms by virtue of being bigger.
They burn more calories overall, but tend to have a lower resting metabolism per body weight, which is specifically what lower metabolism means in this context.
This is a really important aspect here. I am skeptical of efforts to lower the standard human body temp, because it seems to me like normalizing hypothyroidism and other metabolic disorders that, if taken seriously and treated would improve energy levels and quality of life.
Is it possible that thermometer calibration has just drifted slightly over the last couple hundred years? If you told me that the typical electronic thermometer today actually measured around a degree different than the mercury thermometer Wunderlich presumably used, I wouldn't be all too surprised.

Or is there really an accurate and consistent calibration technique that's been in use since at least the 1800s, so we know for sure that it must be humans themselves getting cooler?

Uh surely "mmHg" is a stable unit of measurement where the calibration is self-evident by its own definition.
mmHg is a unit of pressure, not temperature. Mercury thermometers do need to be calibrated.
freezing point of water/boiling point of water are pretty stable temperature checkpoints, once we learned to fix pressure and contamination....
(comment deleted)
The whole enterprise of trying to find "a normal" temperature seems silly to me, increasingly after getting two kids with fevers every now and then.

We use both high-quality ear canal and anal thermometers, and while we have enough statistical grounds to unbias their results compared to each other, there remains significant variance. I.e. if we use an anal or ear canal thermometer makes temperature vary ±0.4 °C.

Then how sloppily you take the measurement with the same thermometer can result in a ±0.2 °C difference for the butt, and ±0.6 °C for the ear canal.

Of course, the time of day we take the temperature can give us a ±0.5 °C difference, and the activity level of the person something like a ±1 °C difference (we don't have as much data on these last ones, naturally.)

And all this is before you bring in the fever! So all of this we consider normal.

Basically, in our experience, anything below 38.4 °C could just as well be caused by any of a number of non-fever conditions at something like a 90 % confidence level, so unless there's a strong prior of fever, a "non-normal" temperature reading on its own is a fairly weak signal.

...which brings me to my final point: the prior ought to strongly affect what counts as normal temperature, but all of this discussion ignores it.

There's also the question whether you prefer false positives or false negatives when it comes to fever detection. My impression is that the medical community prefers false negatives, i.e. pretending that people with a low fever are perfectly normal -- but a lot of private persons I talk to have the opposite preference: they would prefer to think of someone as sick even though they are healthy.

Like any good medical test, you pick a threshold based on what probability you want for false positives and negatives, and you weigh the prior into this judgment. Just investigating what an average resting temperature with a particular measurement method seems to me silly.

> if we use an anal or ear canal thermometer makes temperature vary ±0.4 °C.

This part is just known, though: the usual "close enough" standard for core temperature is an anal temperature and everything else you have to adjust. (Everything else you say I agree with, though.)

I know that's common wisdom, but I also have started to doubt it -- when variation is so large, does it really matter whether you measure in the ear or the butt?

(For what it's worth, my local hospitals use ear canal temperatures for diagnostic purposes.)

Of course it does matter, look up systematic error and random error.
Before being very dismissive, please consider the alternative that I do know about the things you mention, and that there are other ways of looking at the situation.

1. If the ear temperature are consistently wrong (systematic error) it is very easy to debias them and they become equivalent (modulo random error) to anal temperatures.

2. Perhaps cephalic temperature is a better diagnostic tool than gut temperature to evaluate the effects of fever? After all, the brain is a more sensitive organ than the butt.

> the brain is a more sensitive organ than the butt

The more time I spend on the internet, the less certain of this I become.

Anecdotal, but my family has a history of autoimmune disease (including multiple myeloma in my father’s case). My temp is always slightly higher than what is considered normal. It could be due to how my immune system tends to be overactive, many doctors have claimed it is caused by having “connective tissue disease”. Never had any adverse health problems from it.
Just to push back at the anecdote, another anecdote: I personally have an autoimmune disease (MS, in particular, with overactive immune system) and my body temperature has run low for most of my life.
I applaud your accuracy when measuring your kids' temperature. My approach when figuring out if my kids are sick is if their temperature is "high" and their general appearance and conditition is out of the ordinary. The exact decimal of the temperature doesn't matter too much by itself.
We didn't always care to this accuracy. We just used the anal temperature and went on with our day. Then we got the ear canal thermometer for convenience and discovered that the result was not what we expected, so I got curious and started keeping detailed records...

But in the end, I want to get to the point where you are, using a rough rule of thumb. I'm just taking the evidence-based route there!

Hah! I just now realised the English word is "rectal" not "anal" but it seems my comment influenced plenty of other people to use the wrong word too!
Only an anal person would care. You’re good.
The name matters much less than making sure you don’t get the various thermometers confused.
> The exact decimal of the temperature doesn't matter too much by itself.

Indeed, this pseudo-accuracy seems pointless.

The only relevant conclusions that taking the temperature can deliver is whether, a) there is no fever, b) there is a mild fever not requiring major concern, c) there is a major fever and extra care needs to be taken. No one in their right mind would classify these differences based on sub-degree differences in temperature.

No, but it would be cool in the nerdy sense to have a dataset of average temperatures in various conditions, or at least e.g. people are within 98-99f about 60% of the time, within 97.5-99.5 about 90% of the time, within 97-101 about 97% of the time etc, as measured by X device/method at Y time of day after "average" activity level etc.

Instead of just giving temperature, a thermometer could say "there is a 70% chance that your immune system is more active than usual" etc

Of course, small additional data points like "i'm exhausted and coughing more than usual" increase the confidence of the result by orders of magnitude over just temperature...

Anecdotally, after measuring my armpit temperature a number of times in recent years due to checks for covid, I'm close to 36 C or even lower than that. In all my adult life I could deal with anything lower than 38 C without drugs. I would stay warm, rest, sleep on it and be good the next day. I start worrying if it gets past 38.
With our infant using a digital thermometer in the ear, we routinely observe that the left ear is hotter than the right. We take 3 measurements in each ear, we see a similar variance as you mention per ear. Have you observed a similar difference? As adults with the same device we don't see a difference in our own ears.
Sometimes the ears differ, and we use the warmer of the temperatures as our final measurement, as per the instruction booklet of the thermometer. I have not stopped to consider whether this is a consistent chirality bias or just noise!
Maybe it depends on if your child is left brained or right brained (just kidding)
I wonder if taking a temperature after laying in your side sleeping would noticeably change based on which ear you were sleeping on.
These kinds of things make me wonder about body asymmetries - like which side the heart is on, and left/right handedness.
I wouldn't have thought a fever is of sufficient concern that it would warrant sticking a thermometer up your childs arse.
Why? It is easier than getting a toddler to hold it under their tongue and is very accurate.
Women with natural menstrual cycles have a 0.2-0.5 °C higher body temperature after their ovulation because of the higher progesterone level in their blood. They literally don’t have a single "correct" body temperature.

It’s not mentioned in the article, which I find odd, because it tells you something about averaging statistics and male body bias in science.

A lot of it is chosen male because female body is more complicated in some ways. We are just figuring things out with statistics and some things will be wrong if we cut out 50% of the population.

Sience is starting to wake up to this though, but slowly.

When I grew up I've always been told that the "normal" temperature is 36.6 C, which is much closer to the value from this article than 37 C.
Perhaps the temperature of the perfectly healthy state can vary between people as can their sensitivity to deviations. As for me, though, it has always been exactly 36.6°C. The idea of somebody telling me 37°C is healthy drives me mad because I feel terrible at 37°C, such temperature indicates I am surely sick and will probably infect others. As soon as my temperature deviates from 36.6°C (36.65°C is Ok, 36.7°C is not) I immediately feel physical discomfort in my whole body and that is not a placebo effect - I feel it first and confirm it with a measurement after.

I measure my temperature in my armpit using a classic mercury thermometer. I tried an electronic thermometer but found it imprecise.

This way I want to defend 36.6°C as the normal temperature and to abolish 37°C being considered normal as well. Perhaps it can be normal but that would be an individual trait of a specific person. Unless such a temperature is proven normal for this specific person, a person with 37°C armpit temperature should not be allowed to visit the office, attend flights etc.

Uncharitable reading: People are getting fatter and more sedentiary, lowering the normal body temperature. More than ever, we need a distinction between normal and healthy.
People worry too much about temperature/fever, if you have efever (clearly) caused by infection anything below 40.6C is fine and safe and fever reducing drugs are just to make you more comfortable, but they don't really lower any danger.

It's common myth people thinking their kids brain can get fried from infection, which is pretty much impossible, it can get fried from overheating in hot enviroment, but it's pretty much impossible just from infection.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4145646/

In the afternoon my son’s temperature is closer to 99.5. Of course I never measured it unless I thought he was sick and confirmation bias led me to believe he was feverish. I finally started checking it in the afternoon when he seemed well and realized he was just always warm in the afternoon and all that worrying about his “fever” was pointless.
I want to see a study where they bring in people, measure their temperature, then have them walk a mile then measure their temperature again. The decrease seems small enough that it could completely be an artifact of point-in-time activity levels. Everyone drives to the appointment now where two centuries ago they would've probably walked.