You lose most of your body heat out of your head—that’s why your mom always told you
to wear a hat when you went outside in winter.
But why exactly would you lose more heat through your head than some other body part?
Does your brain really generate that much energy and need to emit excess heat as a result?
Hi, I’m Justin Dodd, welcome to misconceptions.
Considering how familiar we all are with the human body, since we all, ya know, have one,
there are a surprising number of enduring misconceptions about it, from our five senses
to the oft-quoted “normal” human body temperature of 98.6 degrees Fahrenheit.
Let’s dive in.
As you probably guessed by the preceding graphic—all things being equal, you don’t actually lose
a disproportionate amount of body heat through your head.
Rachel C. Vreeman and Aaron E. Carroll, both pediatricians, looked into the origins of
this misconception in a humorous 2008 BMJ paper.
They found that the heat-lost-through-your-head concept had been widely adopted by 1970.
A U.S. Army survival manual issued that year recommended wearing hats in cold weather because
“40 to 45 percent of body heat” is lost through a person’s noggin.
That figure apparently came from Army research conducted during the Cold War, a period of
geopolitical tension set off, I wanna say, by a disagreement about the merits of wearing
a beanie in December?
I don’t really remember.
Maybe check out our episode on Misconceptions about the Cold War to fact-check that.
According to hypothermia expert Daniel I. Sessler, during that now decades-old experiment,
scientists dressed volunteers in cold weather survival suits and subjected them to freezing
temperatures, after which the researchers evaluated the performance of the suits.
It appeared that a significant percentage of body heat was lost through the head—but
as Vreeland and Carroll noted in 2008, the suits didn’t include hats.
“Because [the head] was the only part of the subjects’ bodies that was exposed to
the cold, they lost the most heat through their heads,” they reported.
If the same experiment had been done with the unfortunate volunteers wearing nothing
but bathing suits, the head would not have contributed to more than 10 percent of the
body’s heat loss.
A 2006 study submerged eight participants’ heads in cold water and came up with essentially
the same conclusion.
After evaluating the effects of the dunking, researchers found that “the head does not
contribute relatively more than the rest of the body to surface heat loss.”
But that doesn’t mean winter hats are worthless.
Though surface body heat loss may be consistent for any uncovered body part, there is reason
to believe that colder heads lead to disproportionately colder core body temperatures.
This might be because you have more close-to-the-surface blood vessels in your head, or it might be
because you don’t tend to shiver when only your head is cold, meaning you lose out on
shivering’s warming effect.
Did you know shivering warmed you up?
The body is amazing and weird.
If we’ve learned anything from having our body temperature examined by total strangers
at restaurants during the last few years, it’s that 98.6°F is normal.
Anything hotter than that means you’re not only going to miss dinner, but also have an
upcoming date with an uncomfortably long cotton swab.
Actually, we’ve known for at least the past 25 years that the 98.6°F standard is a myth.
So where did that curiously precise number come from?
Back in the mid-19th century, German physician Carl Wunderlich sought to understand how body
temperature related to disease.
At a hospital in Leipzig, where he was the medical director, Wunderlich took patients’
temperatures with a foot-long thermometer stuck into their armpits—over a million
measurements in all.
From there, he determined what he deemed the “average normal temperature of the healthy
human body.”
In his 1868 treatise On the Temperature in Diseases, he wrote that a fundamental principle
of medical thermometry was that healthy human body temp varied between 37° [98.6°F] and
37.5° Celsius [99.5°F]—noting that the temperature of an armpit was closer to 37,
and that of “the rectum or vagina” was a few tenths of a degree higher.
He also suggested as the threshold of fever, indicating the presence of disease.
The 98.6 figure that Americans are familiar with, which seems so oddly specific, is just
the result of converting to Fahrenheit—it may give a misleading perception of precision
for what was, originally, a range of fairly round numbers.
But that may not be the only problem with citing Wunderlich as the final word on body
temperature.
In the 1990s, a professor of medicine at the University of Maryland thought Wunderlich’s
number sounded a little too precise.
Philip Mackowiak borrowed one of Wunderlich’s thermometers from the Mütter Museum in Philadelphia,
and his suspicions grew.
He saw that the temperature could be read only after the instrument had been in place
for 20 minutes.
He also believed that the armpit was a much less reliable locale for accurate measurements
compared to the mouth or rectum.
And, when he examined the accuracy of the instrument’s readings, Mackowiak found them
to be several degrees off.
In his 1994 paper revisiting Wunderlich’s findings, Mackowiak cited a 1950 study that
noted differences in quote-unquote normal temperatures in the morning and at night,
neither one of which was as high as 98.6.
In Mackowiak’s own analysis of 700 temperature readings from 148 adults at the University
of Maryland, only 8 percent of the readings were 98.6.
In this group, he wrote, “98.6°F was not the overall mean temperature, the mean temperature
of any particular time of day, the median temperature, or the single most frequently
recorded temperature.”
Any similarly rigid standard for body temperature in Celsius, without accounting for healthy
variation, would be similarly misleading.
And recent studies have pointed to another potentially confounding variable—human beings
may be literally cooling over time.
A 2020 paper looked at body temperature databases from the Civil War era up until 2017 and found
a drop of 0.03 degrees Celsius per decade.
According to New Scientist, it’s possible that “Modern people have fewer infections,
thanks to vaccines and antibiotics, so our immune systems are less active and our body
tissues less inflamed.”
I should note that we’re still in the early stages of this research, and not all experts
are convinced the trend is real.
I, for one, refuse to believe my great-great-grandpa was hotter than me.
You’d think that something as fundamental as the number of bones in a human skeleton
would be easy to figure out.
You would be wrong.
Scientists have been counting our clavicles and tallying our tibias for thousands of years,
but they haven’t always been able to agree on what that total number is.
According to a communication in the journal Clinical Anatomy, Medieval Europeans thought
there were 248 bones.
In 1543, the Padua surgeon Andreas Vesalius revised that number to a little over 300.
In 1732 the best estimates pegged it at 245, and then in 1858 we finally got to the modern
206 thanks to Henry Gray of Gray’s Anatomy—the reference book, not the TV show, which I believe
only debuted in the late 1890s.
You could write all that off as scientific progress—we had an erroneous idea, and supplanted
it with better information: people have 206 bones.
But, as the dreamy doctors of Seattle Grace Hospital could no doubt tell us, not every
human has 206 bones—far from it, in fact.
Babies are born with more than 300 soft bones, mostly made of cartilage, connected by a tissue
of cells called osteoblasts.
These cells emit a sticky goo of collagen and sugar molecules that traps inorganic minerals.
When enough of the minerals are caught in the gluey tissue, they harden and form compact
bone—the type that provides our skeleton’s structure.
As they grow, an infant’s cartilage-based bones will dissolve and be replaced by clumps
of osteoblasts that foster bone growth.
Many cartilaginous bones will fuse through the process of mineralization, reducing the
total number of bones in the process.
In the limbs, bone formation continues through childhood and adolescence, and finally ends
when the bones have reached their adult length.
You may know that a newborn’s skull consists of several sections that eventually fuse together.
If you look at an adult human skull, you can see the lines, called sutures, where these
plates meet.
So that’s how we go from 300 or so rubbery baby bones to the usual 206 mature bones.
But not even every adult has that exact number.
For example, people can be born with an extra set of ribs accompanying the normal 12.
These “supernumerary ribs” are usually found along the lumbar vertebrae—those in
the lower back—and typically go unnoticed until a person is X-rayed or autopsied.
There's no scientific consensus on how common these extra ribs are, with estimates ranging
from less than 1% to as much as 16% of the population having them.
Another phenomenon in which humans sport extra bones is polydactyly, or extra digits.
You might have heard of Ernest Hemingway’s famous polydactyl cats, which have six toes
instead of five on their front paws.
Polydactyl humans can have an extra finger or toe on one or both extremities, usually
due to mutations on one of several genes.
The extra digits are most often located next to the outer digit—the pinky finger or little
toe—though supernumerary thumbs and other fingers have been documented.
These digits can sport extra bones, though not always a full set.
Polydactyly is surprisingly common—it affects about one in every 700 to 1000 babies.
Devendra Suthar of India holds the Guinness World Record for the most supernumerary digits
with 14 fingers and 14 toes.
For much of human history, humans were believed to have five senses: sight, smell, taste,
hearing, and touch.
This idea can be tied to Aristotle.
In his treatise on the nature of the soul, titled De Anima and written around 350 BCE,
he argued that humans have five special senses, divided into two categories.
He considered touch and taste to be senses that were perceived through direct contact.
Sight, smell, and hearing were accomplished through a medium, in Aristotle’s understanding—either
air or water— which corresponded to two of the four elements that ancient Greeks believed
made up the universe.
In addition, Aristotle noted that each sense had its own designated organ, such as the
nose for smell, which he felt further supported his theory of exactly five senses.
Today, scientists believe humans have many more senses than the basic five.
Proprioception, for example, is the sense of knowing where our body parts are and what
they’re doing.
This sense makes it possible to run without staring at our feet or to pick up an object
without looking at it.
Equilibrioception is basically our sense of balance, which allows us to stand upright
and bend over without falling, not to mention the ability to walk slacklines in public parks
while your friends look on, bored.
Chronoception is our sense of time passing.
And like the number of bones in the human body, the different senses can sometimes join
or overlap.
Synesthesia is a well-known phenomenon in which people say they can see sounds, hear
shapes, or even feel mathematical equations.
Research suggests that synesthesia runs in families, pointing to a genetic component,
but its cause is still not well understood.
As much as 4 percent of the population has gene variants that might be connected to synesthesia—including
such famous synesthetes as novelist Vladimir Nabokov and musician Duke Ellington, along
with, perhaps, artist Vincent van Gogh.
And of course, Bruce Willis might have something to say about another sense, but our fact-checker
hasn’t gotten back to us about the validity of that one.
My chronoception is telling me that we’re out of time.
Is there a question YOU have about the human body?
Drop it in the comments below.
Thanks for watching misconceptions, and I’ll see ya next time.