March 30, 2026 • 10 mins
When you shiver, your fingers and toes go numb, or you get goosebumps in the cold, that's actually your body trying to keep you warm. Learn how it works -- and how you habituate to chilly temperatures over time -- in this episode of BrainStuff, based on this article: https://health.howstuffworks.com/human-body/systems/nervous-system/body-learn-frigid-temperatures.htm
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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff. Lauren Vogelbaum.
Here picture a brisk morning at the sandy shore of
San Francisco Bay. Tony Gilbert is not a former Olympian swimmer.
He's not part of a super athlete team, though he
knows swimmers like that, and he's not wearing a wetsuit.
(00:25):
In his usual swim trunk, swim cap, earplugs and goggles,
Gilbert wades into the forty six degree fahrenheit water that's
seven degrees celsius, and swims out into the murky Bay.
Gilbert is a hobby cold water swimmer. He's been doing
it for over a decade. He returns to shore some
forty minutes later, exhilarated for the article. This episode is
(00:49):
based on haws toff Work spoke with Gilbert back in
twenty twenty two. He said, it's really cold, but we
wouldn't do it if it wasn't fun. It's invigorating. Really.
The first few minutes are still the worst. Then you
get going, the endorphins kick in and you love it.
Gilbert is one of the members of the South End
(01:09):
Rowing Club, founded in eighteen seventy three. Who regularly take
dips in the frigid bay for fun. Gilbert's swims usually
range from twenty to forty minutes, but he's gone as
long as ninety minutes. The curious onlookers might wonder how
he doesn't experience hypothermia or why he actually enjoys swimming
(01:29):
in such cold waters. It turns out that the human
body has evolved some pretty helpful tools to acclimate two
different kinds of cold stress when necessary, depending on the frequency, duration,
and severity of the cold experienced. Basically, when we need
to move around and be comfortable in non life threatening
(01:51):
chili conditions, our bodies can habituate to the cold. When
the cold gets a little more serious, we can go
through more intense adaptations. To talk about all this, first,
let's go over how your body tries to protect you
when you experience cold. Okay, human beings are warm blooded mammals,
(02:12):
which means that we thermoregulate to keep a stable internal
body temperature, usually a little warmer than our environment at
which our organs and systems function well. For most humans,
that internal or core body temperature is right around ninety
seven to ninety nine degrees fahrenheit, which is thirty six
point one to thirty seven point two celsius. We are
(02:36):
able to stay right at that temperature because well, a
we've invented things like clothes, but b our digestive system
and cells break down the food we eat and metabolize
the glucose in it into a compound that our cells
can use for energy called adenisine triphosphate or ATP, and
heat is a byproduct. When you get too cold, like
(02:59):
your body temperature drops below ninety five degrees fahrenheit or
thirty five celsius, your organs can't function and begin to
shut down, which is bad. This is the aforementioned hypothermia,
and it can kill you. So when your body detects
a drop in temperature, it has a few defensive measures
it'll take to keep your core warm. You might start shivering.
(03:24):
This is an involuntary type of muscle contractions that start
in the torso and move to the limbs. What's happening
here is your body is attempting to create more internal heat.
Your muscles produce some heat whenever they contract through a
complicated biomechanical process that I don't understand very well. But
this is why moving around can help you warm up.
(03:48):
But more importantly for shivering, those repeated and rapid contractions
use up ATP real fast, prompting your cells to metabolize
more glucose into ATP plus heat. Of course, your skin
is one of the first line systems that your body
has to sense the cold, and it has a couple
of tricks to pull too. It might go over in goosebumps,
(04:10):
which is another type of involuntary muscle contraction, but instead
of big muscles giving you big shivers, these are tiny
muscles contracting in your skin to generate a bit of
heat and raise up your hair follicles, thus trapping a
bit of air near the skin and thus holding on
to a little bit of body heat. This might have
a negligible effect in humans and work out better for
(04:32):
our furrier cousins. But your skin can also perform another
involuntary function called cutaneous vasoconstriction. That means vascular constriction in
your skin. That is, your blood vessels contract, letting less
blood flow through them at your skin level. You shed
heat through your skin, and especially via blood flowing close
(04:53):
to skin level, so cutaneous vaso constriction keeps that blood
and thus that heat closer into your core to keep
your inner organs warm. This is why your extremities your
hands and feet get cold the fastest in chili conditions.
Your body is trying to keep its heat towards your core.
In these our modern times, we tend to moderate the
(05:17):
amount of cold that we're exposed to by bundling up
and spending more time in heated indoor areas. But even
when we only dip into cold temperatures briefly, even with
a minimum of skin exposed, our bodies can habituate to it.
We experience habituation, for example, over the course of several
cold mornings during ten minute dashes out for coffee or
(05:39):
to walk the dog. Habituations are like physical memory. Instead
of wasting valuable bodily energy sending up red flags to
your central nervous system. Every time your body is exposed
to a cold event, your body remembers it and responds less.
Over time, you won't shiver as much, and your skin
(05:59):
and extras will stay warmer for longer because your body
won't immediately draw blood inward to protect those vital organs. Basically,
your body realizes that the cold isn't going to seriously
damage you and that's also not going away, so it
adjusts to let you function better in the midst of it.
And it's a lot easier to function when you're not
(06:21):
shivering and your fingers aren't numb. This is how cold
water swimmers can tolerate near freezing water. They habituate to it,
but a swimmer can't adjust to swimming long lengths and
cold waters on their first trip. Gilbert said, you have
to be regular, consistent with cold water swimming to stay acclimated.
(06:42):
You have to swim two to three days a week
to stay acclimated, and the few times I did have
a break or fall off schedule, I would start back
at square one. Start with a short ten minute swim
one day, and then the next day try fifteen twenty,
and then back to thirty or forty five minutes. Even
the best, most adjusted swimmers get too cold and have
(07:04):
to stop when their body tells them it's time. Gilbert said,
your body keeps warm at the core, so your extremities
can get cold, especially your fingers are toes. On longer swims,
you'll even see some people get a claw hand or
some people get numb in the lips for a few
minutes and slur their words when they get out of
the water. This, by the way, is part of why
(07:26):
cold water swimmers swim with buddies of form clubs and
enlist more experienced swimmers to help teach new hobbyists how
to stay safe. If you're interested, definitely look into organizations
in your area. Anyway, Over the past couple of decades,
researchers have been looking into another way that our bodies
protect us from the cold. It turns out that shivering
(07:49):
is not the only cold induced way that our bodies
have of producing heat to warm us up. Enter brown fat. Now,
body fat in general is a good insulator and can
help your core stay warm, but there are different kinds
of body fat, white, brown, and beige. A white fat
(08:09):
is the kind you probably think of when you think
of body fat. It's made up of cells that store
lipids to cushion and insulate our innerds and to save
potential energy for a rainy day. It's creamy white in
color because each cell is basically just an envelope of lipids,
with the cells operative equipment the nucleus and mitochondria squished
(08:30):
out to the sides. Brown and beige fat are so
named because they contain a lot more rusty colored, iron
rich mitochondria at giving the cells a brown or beige color.
When you regularly experience cold, your body starts to activate
brown and beige fat cells to basically burn their lipid
stores in order to produce heat. For the article, this
(08:55):
episode is based on how stuff Works. Spoke with Te
Chung Lin, a PhD and Associate professor of biomedical research
at the Masonic Medical Research Institute. He said brown fat
serves as a fireplace in our body to keep us warm.
Individuals regularly exposed to cold, such as winter swimmers, have
higher heat generation efficiency than normal healthy individuals. Some scientists
(09:21):
argue that brown fat evolved early on in mammals and
helped give us a leg up from other species. Human
babies are born with a lot of brown fat to
protect them from cold at birth. Adults tend to retain
a little brown fat stored mostly between our shoulder blades.
Beige fat cells, meanwhile, seem to arise within populations of
(09:42):
white fat cells due to things like cold stress, and
then go about burning off their stored energy to help
keep the body warm. Researchers are still looking into how
brown and beige fat work and how they might be
connected to health factors like blood press usure and blood
sugar regulation. There's a hope that if we could figure
(10:05):
out how to boost the action of these fats, it
might help keep people healthier. So maybe those coldwater swimmers
are onto something. Gilbert said, coldwater swimming feels like you're
taking a bite out of life. There's nothing else like it.
(10:26):
Today's episode is based on the article can our Bodies
Learn to withstand frigid Temperatures? On how stuff works dot com,
written by Alison Troutner. Brain Stuff is production of iHeartRadio
in partnership with how Stuffworks dot Com, and it is
produced by Tyler Klin. Four more podcasts from my heart
Radio visit the iHeartRadio app, Apple Podcasts, or wherever you
listen to your favorite shows.
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff. Lauren Vogelbaum.
Here picture a brisk morning at the sandy shore of
San Francisco Bay. Tony Gilbert is not a former Olympian swimmer.
He's not part of a super athlete team, though he
knows swimmers like that, and he's not wearing a wetsuit.
(00:25):
In his usual swim trunk, swim cap, earplugs and goggles,
Gilbert wades into the forty six degree fahrenheit water that's
seven degrees celsius, and swims out into the murky Bay.
Gilbert is a hobby cold water swimmer. He's been doing
it for over a decade. He returns to shore some
forty minutes later, exhilarated for the article. This episode is
(00:49):
based on haws toff Work spoke with Gilbert back in
twenty twenty two. He said, it's really cold, but we
wouldn't do it if it wasn't fun. It's invigorating. Really.
The first few minutes are still the worst. Then you
get going, the endorphins kick in and you love it.
Gilbert is one of the members of the South End
(01:09):
Rowing Club, founded in eighteen seventy three. Who regularly take
dips in the frigid bay for fun. Gilbert's swims usually
range from twenty to forty minutes, but he's gone as
long as ninety minutes. The curious onlookers might wonder how
he doesn't experience hypothermia or why he actually enjoys swimming
(01:29):
in such cold waters. It turns out that the human
body has evolved some pretty helpful tools to acclimate two
different kinds of cold stress when necessary, depending on the frequency, duration,
and severity of the cold experienced. Basically, when we need
to move around and be comfortable in non life threatening
(01:51):
chili conditions, our bodies can habituate to the cold. When
the cold gets a little more serious, we can go
through more intense adaptations. To talk about all this, first,
let's go over how your body tries to protect you
when you experience cold. Okay, human beings are warm blooded mammals,
(02:12):
which means that we thermoregulate to keep a stable internal
body temperature, usually a little warmer than our environment at
which our organs and systems function well. For most humans,
that internal or core body temperature is right around ninety
seven to ninety nine degrees fahrenheit, which is thirty six
point one to thirty seven point two celsius. We are
(02:36):
able to stay right at that temperature because well, a
we've invented things like clothes, but b our digestive system
and cells break down the food we eat and metabolize
the glucose in it into a compound that our cells
can use for energy called adenisine triphosphate or ATP, and
heat is a byproduct. When you get too cold, like
(02:59):
your body temperature drops below ninety five degrees fahrenheit or
thirty five celsius, your organs can't function and begin to
shut down, which is bad. This is the aforementioned hypothermia,
and it can kill you. So when your body detects
a drop in temperature, it has a few defensive measures
it'll take to keep your core warm. You might start shivering.
(03:24):
This is an involuntary type of muscle contractions that start
in the torso and move to the limbs. What's happening
here is your body is attempting to create more internal heat.
Your muscles produce some heat whenever they contract through a
complicated biomechanical process that I don't understand very well. But
this is why moving around can help you warm up.
(03:48):
But more importantly for shivering, those repeated and rapid contractions
use up ATP real fast, prompting your cells to metabolize
more glucose into ATP plus heat. Of course, your skin
is one of the first line systems that your body
has to sense the cold, and it has a couple
of tricks to pull too. It might go over in goosebumps,
(04:10):
which is another type of involuntary muscle contraction, but instead
of big muscles giving you big shivers, these are tiny
muscles contracting in your skin to generate a bit of
heat and raise up your hair follicles, thus trapping a
bit of air near the skin and thus holding on
to a little bit of body heat. This might have
a negligible effect in humans and work out better for
(04:32):
our furrier cousins. But your skin can also perform another
involuntary function called cutaneous vasoconstriction. That means vascular constriction in
your skin. That is, your blood vessels contract, letting less
blood flow through them at your skin level. You shed
heat through your skin, and especially via blood flowing close
(04:53):
to skin level, so cutaneous vaso constriction keeps that blood
and thus that heat closer into your core to keep
your inner organs warm. This is why your extremities your
hands and feet get cold the fastest in chili conditions.
Your body is trying to keep its heat towards your core.
In these our modern times, we tend to moderate the
(05:17):
amount of cold that we're exposed to by bundling up
and spending more time in heated indoor areas. But even
when we only dip into cold temperatures briefly, even with
a minimum of skin exposed, our bodies can habituate to it.
We experience habituation, for example, over the course of several
cold mornings during ten minute dashes out for coffee or
(05:39):
to walk the dog. Habituations are like physical memory. Instead
of wasting valuable bodily energy sending up red flags to
your central nervous system. Every time your body is exposed
to a cold event, your body remembers it and responds less.
Over time, you won't shiver as much, and your skin
(05:59):
and extras will stay warmer for longer because your body
won't immediately draw blood inward to protect those vital organs. Basically,
your body realizes that the cold isn't going to seriously
damage you and that's also not going away, so it
adjusts to let you function better in the midst of it.
And it's a lot easier to function when you're not
(06:21):
shivering and your fingers aren't numb. This is how cold
water swimmers can tolerate near freezing water. They habituate to it,
but a swimmer can't adjust to swimming long lengths and
cold waters on their first trip. Gilbert said, you have
to be regular, consistent with cold water swimming to stay acclimated.
(06:42):
You have to swim two to three days a week
to stay acclimated, and the few times I did have
a break or fall off schedule, I would start back
at square one. Start with a short ten minute swim
one day, and then the next day try fifteen twenty,
and then back to thirty or forty five minutes. Even
the best, most adjusted swimmers get too cold and have
(07:04):
to stop when their body tells them it's time. Gilbert said,
your body keeps warm at the core, so your extremities
can get cold, especially your fingers are toes. On longer swims,
you'll even see some people get a claw hand or
some people get numb in the lips for a few
minutes and slur their words when they get out of
the water. This, by the way, is part of why
(07:26):
cold water swimmers swim with buddies of form clubs and
enlist more experienced swimmers to help teach new hobbyists how
to stay safe. If you're interested, definitely look into organizations
in your area. Anyway, Over the past couple of decades,
researchers have been looking into another way that our bodies
protect us from the cold. It turns out that shivering
(07:49):
is not the only cold induced way that our bodies
have of producing heat to warm us up. Enter brown fat. Now,
body fat in general is a good insulator and can
help your core stay warm, but there are different kinds
of body fat, white, brown, and beige. A white fat
(08:09):
is the kind you probably think of when you think
of body fat. It's made up of cells that store
lipids to cushion and insulate our innerds and to save
potential energy for a rainy day. It's creamy white in
color because each cell is basically just an envelope of lipids,
with the cells operative equipment the nucleus and mitochondria squished
(08:30):
out to the sides. Brown and beige fat are so
named because they contain a lot more rusty colored, iron
rich mitochondria at giving the cells a brown or beige color.
When you regularly experience cold, your body starts to activate
brown and beige fat cells to basically burn their lipid
stores in order to produce heat. For the article, this
(08:55):
episode is based on how stuff Works. Spoke with Te
Chung Lin, a PhD and Associate professor of biomedical research
at the Masonic Medical Research Institute. He said brown fat
serves as a fireplace in our body to keep us warm.
Individuals regularly exposed to cold, such as winter swimmers, have
higher heat generation efficiency than normal healthy individuals. Some scientists
(09:21):
argue that brown fat evolved early on in mammals and
helped give us a leg up from other species. Human
babies are born with a lot of brown fat to
protect them from cold at birth. Adults tend to retain
a little brown fat stored mostly between our shoulder blades.
Beige fat cells, meanwhile, seem to arise within populations of
(09:42):
white fat cells due to things like cold stress, and
then go about burning off their stored energy to help
keep the body warm. Researchers are still looking into how
brown and beige fat work and how they might be
connected to health factors like blood press usure and blood
sugar regulation. There's a hope that if we could figure
(10:05):
out how to boost the action of these fats, it
might help keep people healthier. So maybe those coldwater swimmers
are onto something. Gilbert said, coldwater swimming feels like you're
taking a bite out of life. There's nothing else like it.
(10:26):
Today's episode is based on the article can our Bodies
Learn to withstand frigid Temperatures? On how stuff works dot com,
written by Alison Troutner. Brain Stuff is production of iHeartRadio
in partnership with how Stuffworks dot Com, and it is
produced by Tyler Klin. Four more podcasts from my heart
Radio visit the iHeartRadio app, Apple Podcasts, or wherever you
listen to your favorite shows.
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Host
Lauren Vogelbaum
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