Your tattoos are inside your immune system,
literally. With each very tasteful piece of art, you kick start a drama with millions of deaths, grand sacrifices and your immune system
stepping in to protect you from yourself. Let's give you a tattoo and zoom in
to see what happens inside your skin. The Conveyor Belt of Death Your skin has to solve a huge problem – it's your
largest organ and has the most direct contact with the world around you. Trillions of microbes, dirt,
insects and vermin can’t be allowed to get inside you – but your skin is also constantly
damaged by you moving through the world. Your body solved this by making your skin a
conveyor belt of death. All the skin you see is actually dead stuff. The alive part of your
skin cells begins around one millimeter deep, in the skin industrial complex. Stem cells
constantly clone themselves producing new skin cells that begin a journey
from the inside to the outside. Each new generation pushes the older ones
further up. As your skin cells mature, they interlock with each other and produce
Lamellar bodies, tiny bags that squirt out fat to create a waterproof coat that
closes any gaps between them. And then, they dry out and kill themselves,
merging together into inseparable lumps. This wall of dead corpses is consistently
pushed upwards. Up to 50 layers of dead cells cover your whole body and are constantly
replaced by new cells moving up. Every hour, you shed around 200,000,000 dead skin cells and
all the dirt or bacteria that are stuck to them. Tattooing this part of your skin would be useless as nothing would stick
around. We need to go deeper. When the Fleshy World Explodes Below the conveyor belt of death lies the
dermis. It's full of structural tissue and cells, tiny blood vessels, sensory cells that report
to nerve endings, the roots of your hairs, sweat glands regulating your temperature.
And of course loads of immune cells, guarding your flesh right
below the moving border wall. This region and below is where
your new tattoo will go. Ok! Ready? The world explodes. Half a dozen monoliths
the size of skyscrapers slam through the fifty layers of dead cells, deep into the dermis,
ripping huge holes into the skin – only to retreat and smash through the tissue again
about twice a second. Tens of thousands of cells are violently killed right away,
ripped into pieces or damaged beyond repair. Luckily, you did your research and chose
a responsible tattoo artist who properly disinfected their tools and your skin. But
you only ever get 99.9% of all bacteria, and some of the survivors made it into your flesh. To put it mildly, your immune system is not
amused at all! All the death and destruction wakes up hundreds of thousands of Macrophages in
your dermis, that rush into the open wounds to defend you. Immediately they start killing
bacteria, release chemicals that call for reinforcements and order your blood vessels to
open up and make your dermis swell up with fluid. But worse than the hundreds of wounds
and a few invaders is the tidal wave of chemicals that floods your tissue. Tattoo
ink can be made from hundreds of substances, some may even be toxic or carcinogenic.
Most are from heavy metals like lead, nickel or chromium dissolved in distilled water. The battlefield is now a wild mix of
dead cell parts, a few panicked bacteria, blood and bodily fluids, platelet
cells trying to close wounds, more and more fresh immune cells
and the flood of tattoo ink. On the scale of your cells, clumps of
ink particles are huge – if you were the size of a cell, they’d range from
big dogs to small office buildings. Your immune system has one main job: Identify
what is not you and smash it until it's dead. The Macrophages are desperately
trying to do that. Like tiny octopuses, they extend arm-like structures and begin
pulling the ink particles inside. Usually, when a Macrophage has eaten an enemy, it showers
it in acid to dissolve it. But this doesn’t work with the ink. They try and try but nothing
works, the particles don't react in any way. And this is just the particles
small enough to be devoured. By now the larger chunks are surrounded
by thousands of your structural skin cells and macrophages that are nomming on them,
bathing them in acid and attack chemicals trying to destroy and kill them. But
they are not moving even a tiny bit. Nothing works! Finally your immune system has to concede. It
will not win this fight – so it does the next best thing: Not lose. Your cells don’t know
how dangerous these metals and chemicals are, but they can at least not let them spread
around. So they just stay in place. They vacuum up all the particles they can fit
into their bodies and surround the larger ones trapping them in the only prison they can
build: themselves. Bit by bit, the ink inside thousands of tiny wounds moves inside millions
of immune cells that freeze in place forever. On the outside you don’t notice any of
this. Your new tattoo is fresh and the colours vibrant. Your skin hurts and is
irritated and swollen. But wounds heal, tiny holes close, dead cells are replaced. Bit
by bit, the conveyor belt of death does its job, shedding dead cells ripe in colour, replacing
them with fresh and clean ones. Your tattoo becomes a little less vibrant, now the ink
is no longer on your skin but inside it. But what you are really seeing
is millions of your Macrophages, sitting in your dermis, patiently holding
the ink in place, protecting your body from poison. Your immune system
is why your tattoo is forever. Actually Nothing is Forever Over time your Macrophages get old and die
and new ones come in to gobble up the ink and keep it in place. But sometimes
a tiny bit of ink escapes. Most of it is recaptured and locked in place,
but not always the exact same place. You notice that as your tattoo fades out a bit
and turns less sharp and crisp at its edges. Some of the ink escapes the tattoo entirely.
It rides fluids flowing from your tissue and spreads around your body, another reason
why tattoo ink should ideally not be poison. Your immune system also kind of doesn’t want
you to remove tattoos – to do that usually the ink is shot at with lasers, which heats up the
particles until they break into smaller chunks, cooking your brave Macrophages in the
process. With every round of lasering, more of your tattoo is broken down and
carried away by fluids. But also every time new Macrophages rush into the tattoo
to lock the ink in place. So like uhm, maybe think about it carefully before you get the
name of your new bae tattooed, but you do you. But if you got one, you can directly see
your immune system protecting you. This is how much your body loves you, which
is kind of sweet. And while tattoos are probably not that big of a deal for your
body if applied correctly: you now know about the struggle going on inside your skin
and the sacrifice of your Macrophage buddies, only for you to have that art forever. To appreciate your amazing immune system, you have to know about it first – and the same
goes for anything going on in our universe. To help you with that, we’ve created a series
of lessons to take your scientific knowledge to the next level. Made in collaboration
with our friends at Brilliant.org, these lessons let you further explore
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