Quick! What's the biggest organ in your body?
You might be surprised to find out it's the skin, which you
might not think of as an organ. No matter how you think of it, your
skin is very important. It covers and protects everything inside
your body. Without skin, people's
muscles
,
bones
, and organs would be hanging out all over the place. Skin holds
everything together. It also:
- protects our bodies
- helps keep our bodies at just the right temperature
- allows us to have the sense of touch
Don't Miss Your Epidermis
The skin is made up of three layers, each with its own important
parts. The layer on the outside is called the
epidermis
(say: eh-puh-
dur
-mis). The epidermis is the part of your skin you can see.
Look down at your hands for a minute. Even though you can't
see anything happening, your epidermis is hard at work. At the
bottom of the epidermis, new skin cells are forming.
When the cells are ready, they start moving toward the top of
your epidermis. This trip takes about 2 weeks to a month. As newer
cells continue to move up, older cells near the top die and rise to
the surface of your skin. What you see on your hands (and
everywhere else on your body) are really dead skin cells.
These old cells are tough and strong, just right for covering
your body and protecting it. But they only stick around for a
little while. Soon, they'll flake off. Though you can't see
it happening, every minute of the day we lose about 30,000 to
40,000 dead skin cells off the surface of our skin.
So just in the time it took you to read this far, you've
probably lost about 40,000 cells. That's almost 9 pounds (4
kilograms) of cells every year! But don't think your skin might
wear out someday. Your epidermis is always making new skin cells
that rise to the top to replace the old ones. Most of the cells in
your epidermis (95%) work to make new skin cells.
And what about the other 5%? They make a substance called
melanin
(say:
meh
-luh-nin). Melanin gives skin its color. The darker your skin is,
the more melanin you have. When you go out into the sun, these
cells make extra melanin to protect you from getting burned by the
sun's ultraviolet, or UV, rays.
That's why your skin gets tan if you spend a lot of time in
the sun. But even though melanin is mighty, it can't shield you
all by itself. You'll want to wear
sunscreen
and protective clothing, such as a hat, to prevent painful
sunburns. Protecting your skin now also can help prevent skin
cancer
when you get older.
The Dermis Is Under the Epidermis
The next layer down is the
dermis
(say:
dur
-mis). You can't see your dermis because it's hidden under
your epidermis. The dermis contains nerve endings, blood vessels,
oil glands, and sweat glands. It also contains collagen and
elastin, which are tough and stretchy.
The
nerve endings
in your dermis tell you how things feel when you touch them. They
work with your
brain
and nervous system, so that your brain gets the message about what
you're touching. Is it the soft fur of a cat or the rough
surface of your skateboard?
Sometimes what you feel is dangerous, so the nerve endings work
with your muscles to keep you from getting hurt. If you touch
something hot, the nerve endings in your dermis respond right away:
"Ouch! That's hot!" The nerves quickly send this
message to the brain or spinal cord, which then immediately
commands the muscles to take your hand away. This all happens in a
split second, without you ever thinking about it.
Your dermis is also full of tiny
blood vessels
. These keep your skin cells healthy by bringing them the oxygen
and nutrients they need and by taking away waste. These blood
vessels are hard to see in kids, but you might get a better look if
you check out your grandparents' skin. As the dermis gets
older, it gets thinner and easier to see through.
The dermis is home to the
oil glands
, too. These are also called
sebaceous
(say: sih-
bay
-shus)
glands
, and they are always producing
sebum
(say:
see
-bum). Sebum is your skin's own natural oil. It rises to the
surface of your epidermis to keep your skin lubricated and
protected. It also makes your skin waterproof - as long as
sebum's on the scene, your skin won't absorb water and get
soggy.
You also have
sweat glands
on your epidermis. Even though you can't feel it, you actually
sweat a tiny bit all the time. The sweat comes up through
pores
(say:
pors
), tiny holes in the skin that allow it to escape. When the sebum
meets the sweat, they form a protective film that's a bit
sticky.
An easy way to see this film in action is to pick up a pin with
your fingers. Then wash your hands well with soap and water and dry
them off completely. Now try to pick up that pin again. It
won't be so easy because your sticky layer is gone! Don't
worry - it will be back soon, as your sebaceous and sweat glands
create more sticky stuff.
The Third Layer Is Subcutaneous Fat
The third and bottom layer of the skin is called the
subcutaneous
(say: sub-kyoo-
tay
-nee-us)
layer
. It is made mostly of fat and helps your body stay warm and absorb
shocks, like if you bang into something or fall down. The
subcutaneous layer also helps hold your skin to all the tissues
underneath it.
This layer is where you'll find the start of
hair
, too. Each hair on your body grows out of a tiny tube in the skin
called a
follicle
(say:
fah
-lih-kul). Every follicle has its roots way down in the
subcutaneous layer and continues up through the dermis.
You have hair follicles all over your body, except on your lips,
the palms of your hands, and the soles of your feet. And you have
more hair follicles in some places than in others - there are more
than 100,000 follicles on your head alone!
Your hair follicles rely on your sebaceous glands to bring on
the shine. Connected to each follicle in the dermis layer is a tiny
sebaceous gland that releases sebum onto the hair. This lightly
coats the hair with oil, giving it some shine and a little
waterproofing.
Skin Can Warm and Cool You
Your skin can help if you're feeling too hot or too cold.
Your blood vessels, hair, and sweat glands cooperate to keep your
body at just the right temperature. If you were to run around in
the heat, you could get overheated. If you play outside when
it's cold, your inner temperature could drop. Either way, your
skin can help.
Your body is pretty smart. It knows how to keep your temperature
right around 98.6 degrees Fahrenheit (37 degrees Celsius) to keep
you and your cells healthy. Your skin can respond to messages sent
out by your
hypothalamus
(say: hi-poh-
thah
-luh-mus), the brain's inner thermometer. If you've been
running around on a hot day, your blood vessels get the signal from
the hypothalamus to release some of your body's heat. They do
this by bringing warm blood closer to the surface of your skin.
That's why you sometimes get a red face when you run
around.
To cool you down, sweat glands also swing into action by making
lots of sweat to release body heat into the air. The hotter you
are, the more sweat your glands make! Once the sweat hits the air,
it evaporates (this means that it changes from a liquid to a vapor)
off your skin, and you cool down.
What about when you're ice-skating or sledding? When
you're cold, your blood vessels keep your body from losing heat
by narrowing as much as possible and keeping the warm blood away
from the skin's surface. You might notice tiny bumps on your
skin. Most kids call these goosebumps, but the fancy name for them
is the
pilomotor
(say:
pie
-low-mo-tur)
reflex
. The reflex makes special tiny muscles called the
erector pili
(say: ee-
rek
-tur
pie
-lie)
muscles
pull on your hairs so they stand up very straight.
Keep It Clean!
Unlike other organs (like your lungs, heart, and brain), your
skin likes a good washing. When you wash your skin, use water and a
mild soap. And don't forget to cover scrapes and cuts with
gauze or a bandage. This keeps the dirt out and helps prevent
infections. It's just one way to be kind to the skin you're
in!
Updated and reviewed by:
Steven Dowshen, MD
Date reviewed: March 2007
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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