Hello. This is 6 Minute English
from BBC Learning English. I'm Rob.
And I'm Georgina.
Brrr! It's freezing cold outside today,
Georgina! Make sure you
wrap up warm.
I'll put my woolly hat on. When I was
growing up I was told that you lose
half your body heat from your head.
Oh, don't believe that, Georgina!
It's just a popular myth - you know,
something people think is true
which actually isn't, 'like bulls get
angry when they see the colour red',
or 'goldfish only have a three-second memory'.
Oh... I thought red really did
make bulls angry! But you're right,
there is some disagreement over
the age-old question: should I wear
a hat when it's cold outside?
In this programme, we'll be asking
how much body heat we lose from
our head and discovering that
a simple answer isn't so easy to
find. But first, it's time for my quiz
question. And let's start by asking
someone who knows all about
surviving in the cold - the US army.
According to the 'Cold Weather
Survival' chapter of the US army
field guide, how much heat is lost in
the cold through an uncovered head?
Is it: a) 30 to 35%?, b) 40 to 45%?
or c) 50 to 55%?
You might say it's just a popular myth,
Rob, but I still think half your body heat
is lost from the head, so
I'll say c) 50 to 55%.
OK, Georgina - we'll come back
to that later. Anyway, whichever answer
is correct, the US army obviously
thinks a large percentage of body heat
escapes through the head.
But that may not be the whole picture.
Over the years, experiments to
measure body temperature in
the snowy wastelands of Canada
and Alaska have given wildly
different results - mostly because
of variations in the methods used,
for example, whether the
volunteer's head was covered or
not, and whether they were dry
or submerged in water.
So maybe the US army's view is
out of date. And here's some surprising
information that Tim Harford, presenter
of BBC World Service programme,
More or Less, found after a quick
search on Google:
The head accounts for about 7% of
the body surface area and the heat loss
is fairly proportional to the amount
of skin that's showing.
A human body's surface area
means the total area of skin on
its outer surfaces - that's the head,
chest - or torso, plus the arms and legs.
According to this view, heat
loss - meaning the total amount of
heat transferred away from something
through its surface, is proportional
to body surface area. In that case,
a 50% heat loss from the head - which
only makes up 7% of the body's
surface area - seems like an overestimation.
In the 1950s, other military experiments
were carried out in Canada on soldiers
wearing artic warfare clothing - the kind
of super-warm thermal clothes you
might wear in sub-zero temperatures -
but with nothing to cover their heads.
Here's professor of physiology,
Mike Tipton, taking up the story
with BBC World Service
programme, More or Less:
The question was: how important
is the head to also provide some
equipment, a hat or some form
of insulation. And in that scenario
of course, when you've got insulation
over much of the rest of the
body preventing heat loss, then
obviously the percentage of heat
loss from the head is going to be high...
and at minus 4 degrees Celsius,
it amounted to about half of the
resting heat production of the body.
Here the soldiers bodies were
protected with insulation - thick
material used to stop heat from escaping.
Since their heads were exposed
to the cold, around half of their body
heat escaped that way when resting -
not moving or doing anything active.
And so the idea that half your body
heat is lost through the head slowly
become a popular myth.
But before you throw your woolly
hats in the bin, there's another
consideration to bear in mind;
one that concerns your core
temperature - that's the internal
temperature inside your body,
including the blood, heart,
and other vital organs.
When the head is allowed to
get cold and the body is well insulated,
the body's core temperature drops
rapidly due to the circulation of blood.
Wow! This question really is
blowing hot and cold - now I have no
idea how much heat is actually lost
from the head! Why don't you just
tell me the answer, Rob?
OK then. Well, in my quiz question
I asked how much heat the US army
guide says is lost through the head.
I guessed c) 50 to 55%, or
roughly one half. Was I right?
Well, you were warm, Georgina -
but not right. In fact the army field
guide says, b) 40 to 45% - but
as we've seen in this case,
cold facts are hard to come by.
Let's recap our vocabulary then,
because we're still not sure if
wearing a hat to keep warm is
just a popular myth - something
people believe to be true but
which actually is not.
It seems that heat loss - the
total heat transferred away from
something, is linked to the surface
area or total area of the body's
outer surfaces when exposed
to the cold.
But wearing insulation - material
used to stop heat from escaping,
may change the body's resting
temperature - its temperature
when not moving and at rest...
... and also affect your core
temperature - your body's internal
temperature, including the heart and blood.
That's all for this programme.
Remember to wrap up warm for the winter...
And maybe pop a woolly hat in
your pocket to wear, just in case!
See you again soon for more
trending topics and vocabulary
here at 6 Minute English.
Bye for now!
Bye!