November 25, 2025 • 10 mins
Our skin is our first line of defense as we move through the world, providing both a physical barrier and an immune barrier against microbes and other dangers that could make us sick. Learn how the skin barrier works in this episode of BrainStuff.
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Episode Transcript
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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff. Lauren
Bobelbam here. If you've ever watched a medieval era drama
or fantasy, you may have marveled at the elaborate armor
that characters wear into battle. Made of plates or scales
(00:22):
or mail, armor is built to protect the wearer from
specific types of weapons and attacks. It may not feel
like it, but your skin is also a type of
incredibly effective armor built to fend off specific attacks. It's
not great at handling swords or arrows, but to be fair,
(00:42):
those are relatively new inventions, far older threats like microbes
and ultraviolet light. That's where our skin is a hero.
It's our first line of defense as we move through
the world, though it operates more like the manned walls
of a castle than armor on a knight. Specialized cells
(01:03):
and surrounding structures form a physical barrier between you and
everything that's not you, sort of like a castle wall,
and inside of that, an immune barrier stands at the
ready like a castle's guard, to eliminate any threats that
do make it through. But for our body's most visible organ.
(01:24):
All of this happens on a microscopic level. So today
let's delve into the skin barrier, how it protects us,
and what can happen when something goes wrong. We've talked
before on the show about the layers of the skin.
The innermost layer, the hypodermis, provides structural support. It contains
fat to insulate and cushion our underlying muscles and organs,
(01:46):
plus blood vessels to get supplies to the middle layer,
the dermis. The dermis contains all of the skin's equipment,
nerve endings, sweat glands, pair follicles, and so on. All
of that is sealed in and protected the outermost layer,
the epidermis. The epidermis itself has two main layers, the
inner of which is living, and the outer of which
(02:08):
is dead. The dead skin cells of the outer layer
are what we see and touch, and it's called the
stratum cornium. The stratum corneum is often described as being
like a brick wall, though luckily for us, a very
flexible one, because it's made up of tough cells that
are stacked and bound together with a kind of mortar
(02:30):
of waxy, fatty lipids and some adhesive proteins. Those tough
cells are called corneocytes. It's weird to think that their
entire purpose in life is to die, but it's for
the greater good of the organism. Because they're dead, they
can't be infected by a virus or stopped from doing
(02:51):
their job by bacteria. At their job is to sit there.
They develop in the inner part of the epidermis, and
as they're pushed to the out side, they die and
flatten into sort of long, hardened envelopes containing keratin. Keratin
is the protein that makes our hair and nails tough,
and other things too, like feathers, hoofs, and horns. The
(03:15):
etymology of the words keratin and corneocyte is actually related
to the word horn. They all root back to early
Indo European words for the hard and bony things that
come off of an animal's skull. It's the same root
where we get the word for the horn shaped cornucopia. Anyway,
the tough corneocytes in your stratum corneum also contains stuff
(03:38):
that can grab up molecules of water, which is good
because ideally your outer skin should be dry. No one
wants permanently moist skin, but not too dry. Having a
bit of water in your skin keeps it pliable and
prevents the skin from cracking. And as I said, the
corneocytes are bound together with the sort of mortar made
(04:01):
up of sticky proteins and a bunch of lipids, which
are fatty or waxy substances. This is great because a
it holds the corneosytes tightly in place, and also b
it's what makes our skin more or less waterproof. Oil
and water repel each other, so the oily lipids help
(04:21):
make our skin impermeable to water. The stratum cornium is
essentially the reason that all of the water that makes
up some sixty percent of our body and makes our
organs work stays in our body and doesn't just evaporate out.
It also prevents many potentially harmful water based liquids, including
ones that contain germs, from leaking into our body. Not
(04:45):
too shabby for a stack of dead cells only some
ten to twenty micrometers thick, which is about the thickness
of one or two layers of plastic wrap. Even the
fact that the corneocytes are dead and thus can't be
repaired when they wear out and therefore get sloughed off
and replaced on a continual basis. That's a feature, not
a bug. This way, any microbes that might take up
(05:09):
residents in or around your corneocytes get slothed right off
with them. In healthy skin, your stratum cornium totally replaces
itself about once a month. The cells in the layer
of the epidermis directly beneath the stratum cornium where the
corneocytes develop, are also tightly junctured together, adding to the
(05:29):
security of the physical barrier of our skin. Plus they
release some helpfully antimicrobial molecules. Because as impressive as this
physical barrier is, it is then and delicate and pretty
easily scratched or pierced. That's why we have an immune
border guard lying in wait just inside our skin's castle wall.
(05:53):
Our immune system is really complicated, and I am not
a medical professional, y'all, I was an English major. But
very basically, your epidermis and dermis each contain some specialized
immune cells that can contain and neutralize any invaders. They
can also call in backup from other immune cells that
exist throughout the body via chemical signaling that creates inflammation.
(06:19):
If you think about the last time you got a
scrape or a cut, you may have noticed that it
got reddish or purplish and puffed up a bit. That
inflammation may be uncomfortable, but it's our body's way of
getting extra supplies to the site of an injury to
prevent infection and heal everything up. Once that backup arrives
(06:39):
to the site, all of the immune cells work together
inside the skin to clear out invaders and cellular debris.
When they're done, other cells call off the inflammation and
everything goes back to normal. The physical barrier is restored,
and the immune barrier steps down from red alert to
a state of watchful preparedness. Of course, this is assuming
(07:03):
that everything is operating normally. The creation of the physical
barrier and the responses of the immune barrier are both
extremely complex processes, and unfortunately, any number of things can
upset them, either from the outside in or the inside out,
or both. Just for example, that lipid mortar around corneocytes
(07:27):
gets produced by the corneocytes themselves as they develop into
their final form. So if anything changes in the cells
developmental process, say if it moves too fast, that doesn't
just disrupt how those corneocyte bricks stack up. It can
also disrupt the formation of the mortar around them, and
having too much or too little of any component in
(07:49):
the bricks or the mortar changes the way that the
wall holds together. From the outside, our skin can become
brittle if our environment is too dry, but it can
also get flaky if it's too humid. Exposure to irritating
or allergenic substances can cause an overactive immune response. Getting
(08:10):
too much sun does cellular damage that your skin has
to repair, which when repeated, will reduce cellular function over time.
Even our mental health and stress levels are tied into
how our organs function, and our skin certainly is an exempt,
as anyone who's ever gotten a ZiT before a big
event can tell you. From the inside, there are a
(08:32):
number of diseases and conditions that muck about with some
part of the skin barrier's upkeep, resulting in itchiness, flakiness,
or other discomfort at best. For example, we talked recently
on the show about psoriasis, a condition in which a
combination of skin cell overgrowth and immune system freak out
(08:52):
creates uncomfortable, scaly, or discolored patches that come and go,
triggered by those outside stressors that I mentioned. If you
or someone in your care experiences chronic skin barrier disruptions
that result in that kind of issue. Definitely talk to
a medical professional about the best way or ways to proceed.
(09:12):
There are lots of topical and systemic treatments that can
help control activity in the immune system or the skin,
and a healthcare provider will be able to help you
with the diagnosis and a plan. That being said, even
finding a regimen that keeps quote unquote normal skin happy
can be a challenge because the skin barrier is so
complex that its exact functions are really pretty unique to
(09:35):
all of us, and it changes over time. Simply getting
older means that our skin structure thins and becomes less
elastic and develops a different balance of immune cells. These
changes in our skin barrier make us more susceptible to infections.
A specialist like a dermatologist or esthetician may be able
(09:56):
to help find exactly the right kind of moisturizer and
other products for you, but the top level advice is
to prevent skin barrier damage in the first place by
treating your skin gently, protect it if you're going to
be handling harsh chemicals or going out in the sun,
and don't over cleanse after all, if your skin is
(10:18):
your castle, your first duty is to respect such a
grand structure. Today's episode is an original written by me.
Brain Stuff is production of iHeartRadio, produced by Tyler Klang.
Four more podcasts 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
Bobelbam here. If you've ever watched a medieval era drama
or fantasy, you may have marveled at the elaborate armor
that characters wear into battle. Made of plates or scales
(00:22):
or mail, armor is built to protect the wearer from
specific types of weapons and attacks. It may not feel
like it, but your skin is also a type of
incredibly effective armor built to fend off specific attacks. It's
not great at handling swords or arrows, but to be fair,
(00:42):
those are relatively new inventions, far older threats like microbes
and ultraviolet light. That's where our skin is a hero.
It's our first line of defense as we move through
the world, though it operates more like the manned walls
of a castle than armor on a knight. Specialized cells
(01:03):
and surrounding structures form a physical barrier between you and
everything that's not you, sort of like a castle wall,
and inside of that, an immune barrier stands at the
ready like a castle's guard, to eliminate any threats that
do make it through. But for our body's most visible organ.
(01:24):
All of this happens on a microscopic level. So today
let's delve into the skin barrier, how it protects us,
and what can happen when something goes wrong. We've talked
before on the show about the layers of the skin.
The innermost layer, the hypodermis, provides structural support. It contains
fat to insulate and cushion our underlying muscles and organs,
(01:46):
plus blood vessels to get supplies to the middle layer,
the dermis. The dermis contains all of the skin's equipment,
nerve endings, sweat glands, pair follicles, and so on. All
of that is sealed in and protected the outermost layer,
the epidermis. The epidermis itself has two main layers, the
inner of which is living, and the outer of which
(02:08):
is dead. The dead skin cells of the outer layer
are what we see and touch, and it's called the
stratum cornium. The stratum corneum is often described as being
like a brick wall, though luckily for us, a very
flexible one, because it's made up of tough cells that
are stacked and bound together with a kind of mortar
(02:30):
of waxy, fatty lipids and some adhesive proteins. Those tough
cells are called corneocytes. It's weird to think that their
entire purpose in life is to die, but it's for
the greater good of the organism. Because they're dead, they
can't be infected by a virus or stopped from doing
(02:51):
their job by bacteria. At their job is to sit there.
They develop in the inner part of the epidermis, and
as they're pushed to the out side, they die and
flatten into sort of long, hardened envelopes containing keratin. Keratin
is the protein that makes our hair and nails tough,
and other things too, like feathers, hoofs, and horns. The
(03:15):
etymology of the words keratin and corneocyte is actually related
to the word horn. They all root back to early
Indo European words for the hard and bony things that
come off of an animal's skull. It's the same root
where we get the word for the horn shaped cornucopia. Anyway,
the tough corneocytes in your stratum corneum also contains stuff
(03:38):
that can grab up molecules of water, which is good
because ideally your outer skin should be dry. No one
wants permanently moist skin, but not too dry. Having a
bit of water in your skin keeps it pliable and
prevents the skin from cracking. And as I said, the
corneocytes are bound together with the sort of mortar made
(04:01):
up of sticky proteins and a bunch of lipids, which
are fatty or waxy substances. This is great because a
it holds the corneosytes tightly in place, and also b
it's what makes our skin more or less waterproof. Oil
and water repel each other, so the oily lipids help
(04:21):
make our skin impermeable to water. The stratum cornium is
essentially the reason that all of the water that makes
up some sixty percent of our body and makes our
organs work stays in our body and doesn't just evaporate out.
It also prevents many potentially harmful water based liquids, including
ones that contain germs, from leaking into our body. Not
(04:45):
too shabby for a stack of dead cells only some
ten to twenty micrometers thick, which is about the thickness
of one or two layers of plastic wrap. Even the
fact that the corneocytes are dead and thus can't be
repaired when they wear out and therefore get sloughed off
and replaced on a continual basis. That's a feature, not
a bug. This way, any microbes that might take up
(05:09):
residents in or around your corneocytes get slothed right off
with them. In healthy skin, your stratum cornium totally replaces
itself about once a month. The cells in the layer
of the epidermis directly beneath the stratum cornium where the
corneocytes develop, are also tightly junctured together, adding to the
(05:29):
security of the physical barrier of our skin. Plus they
release some helpfully antimicrobial molecules. Because as impressive as this
physical barrier is, it is then and delicate and pretty
easily scratched or pierced. That's why we have an immune
border guard lying in wait just inside our skin's castle wall.
(05:53):
Our immune system is really complicated, and I am not
a medical professional, y'all, I was an English major. But
very basically, your epidermis and dermis each contain some specialized
immune cells that can contain and neutralize any invaders. They
can also call in backup from other immune cells that
exist throughout the body via chemical signaling that creates inflammation.
(06:19):
If you think about the last time you got a
scrape or a cut, you may have noticed that it
got reddish or purplish and puffed up a bit. That
inflammation may be uncomfortable, but it's our body's way of
getting extra supplies to the site of an injury to
prevent infection and heal everything up. Once that backup arrives
(06:39):
to the site, all of the immune cells work together
inside the skin to clear out invaders and cellular debris.
When they're done, other cells call off the inflammation and
everything goes back to normal. The physical barrier is restored,
and the immune barrier steps down from red alert to
a state of watchful preparedness. Of course, this is assuming
(07:03):
that everything is operating normally. The creation of the physical
barrier and the responses of the immune barrier are both
extremely complex processes, and unfortunately, any number of things can
upset them, either from the outside in or the inside out,
or both. Just for example, that lipid mortar around corneocytes
(07:27):
gets produced by the corneocytes themselves as they develop into
their final form. So if anything changes in the cells
developmental process, say if it moves too fast, that doesn't
just disrupt how those corneocyte bricks stack up. It can
also disrupt the formation of the mortar around them, and
having too much or too little of any component in
(07:49):
the bricks or the mortar changes the way that the
wall holds together. From the outside, our skin can become
brittle if our environment is too dry, but it can
also get flaky if it's too humid. Exposure to irritating
or allergenic substances can cause an overactive immune response. Getting
(08:10):
too much sun does cellular damage that your skin has
to repair, which when repeated, will reduce cellular function over time.
Even our mental health and stress levels are tied into
how our organs function, and our skin certainly is an exempt,
as anyone who's ever gotten a ZiT before a big
event can tell you. From the inside, there are a
(08:32):
number of diseases and conditions that muck about with some
part of the skin barrier's upkeep, resulting in itchiness, flakiness,
or other discomfort at best. For example, we talked recently
on the show about psoriasis, a condition in which a
combination of skin cell overgrowth and immune system freak out
(08:52):
creates uncomfortable, scaly, or discolored patches that come and go,
triggered by those outside stressors that I mentioned. If you
or someone in your care experiences chronic skin barrier disruptions
that result in that kind of issue. Definitely talk to
a medical professional about the best way or ways to proceed.
(09:12):
There are lots of topical and systemic treatments that can
help control activity in the immune system or the skin,
and a healthcare provider will be able to help you
with the diagnosis and a plan. That being said, even
finding a regimen that keeps quote unquote normal skin happy
can be a challenge because the skin barrier is so
complex that its exact functions are really pretty unique to
(09:35):
all of us, and it changes over time. Simply getting
older means that our skin structure thins and becomes less
elastic and develops a different balance of immune cells. These
changes in our skin barrier make us more susceptible to infections.
A specialist like a dermatologist or esthetician may be able
(09:56):
to help find exactly the right kind of moisturizer and
other products for you, but the top level advice is
to prevent skin barrier damage in the first place by
treating your skin gently, protect it if you're going to
be handling harsh chemicals or going out in the sun,
and don't over cleanse after all, if your skin is
(10:18):
your castle, your first duty is to respect such a
grand structure. Today's episode is an original written by me.
Brain Stuff is production of iHeartRadio, produced by Tyler Klang.
Four more podcasts my heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you listen to your favorite shows.
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