00:00Your tattoos are inside your immune system, literally.
00:05With each very tasteful piece of art, you kickstart a drama with millions of deaths,
00:10grand sacrifices and your immune system stepping in to protect you from yourself.
00:16Let's give you a tattoo and zoom in to see what happens inside your skin.
00:22The conveyor belt of death.
00:25Your skin has to solve a huge problem.
00:28It's your largest organ and has the most direct contact with the world around you.
00:33Trillions of microbes, dirt, insects and vermin can't be allowed to get inside you,
00:38but your skin is also constantly damaged by you moving through the world.
00:43Your body solved this by making your skin a conveyor belt of death.
00:47All the skin you see is actually dead stuff.
00:51The alive part of your skin cells begins around 1 mm deep in the skin industrial complex.
00:58Stem cells constantly clone themselves, producing new skin cells that begin a journey from the
01:02inside to the outside.
01:05Each new generation pushes the older ones further up.
01:08As your skin cells mature, they interlock with each other and produce lamellar bodies, tiny
01:13bags that squirt out fat to create a waterproof coat that closes any gaps between them.
01:19Then they dry out and kill themselves, merging together into inseparable lumps.
01:24This wall of dead corpses is consistently pushed upwards.
01:29Up to 50 layers of dead cells cover your whole body and are constantly replaced by new cells moving up.
01:35Every hour, you shed around 200 million dead skin cells and all the dirt or bacteria that are stuck to them.
01:41Tattooing this part of your skin would be useless as nothing would stick around.
01:47We need to go deeper.
01:49When the fleshy world explodes, below the conveyor belt of death lies the dermis.
01:55It's full of structural tissue and cells, tiny blood vessels, sensory cells that report to nerve endings,
02:00the roots of your hairs, sweat glands regulating your temperature and of course loads of immune cells,
02:07guarding your flesh right below the moving border wall.
02:10This region and below is where your new tattoo will go.
02:14Okay, ready?
02:16The world explodes.
02:18Half a dozen monoliths the size of skyscrapers slam through the 50 layers of dead cells,
02:24deep into the dermis, ripping huge holes into the skin.
02:28Only to retreat and smash through the tissue again about twice a second.
02:32Tens of thousands of cells are violently killed right away,
02:35ripped into pieces or damaged beyond repair.
02:39Luckily, you did your research and chose a responsible tattoo artist
02:43who properly disinfected their tools and your skin.
02:46But you only ever get 99.9% of all bacteria and some of the survivors made it into your flesh.
02:53To put it mildly, your immune system is not amused at all.
02:57All the death and destruction wakes up hundreds of thousands of macrophages in your dermis
03:01that rush into the open wounds to defend you.
03:04Immediately, they start killing bacteria, release chemicals that call for reinforcements,
03:08and order your blood vessels to open up and make your dermis swell up with fluid.
03:13But worse than the hundreds of wounds and a few invaders is the tidal wave of chemicals
03:17that floods your tissue.
03:19Tattoo ink can be made from hundreds of substances, some may even be toxic or carcinogenic.
03:24Most are from heavy metals like lead, nickel or chromium dissolved in distilled water.
03:29The battlefield is now a wild mix of dead cell parts, a few panicked bacteria,
03:35blood and bodily fluids, platelet cells trying to close wounds,
03:38more and more fresh immune cells, and the flood of tattoo ink.
03:43On the scale of your cells, clumps of ink particles are huge.
03:47If you were the size of a cell, they'd range from big dogs to small office buildings.
03:53Your immune system has one main job.
03:55Identify what is not you and smash it until it's dead.
04:00The macrophages are desperately trying to do that.
04:03Like tiny octopuses, they extend arm-like structures and begin pulling the ink particles inside.
04:08Usually, when a macrophage has eaten an enemy, it showers it in acid to dissolve it.
04:13But this doesn't work with the ink.
04:16They try and try, but nothing works.
04:18The particles don't react in any way.
04:21And this is just the particles small enough to be devoured.
04:24By now, the larger chunks are surrounded by thousands of your structural skin cells
04:29and macrophages that are nomming on them, bathing them in acid and attack chemicals,
04:33trying to destroy and kill them.
04:35But they're not moving even a tiny bit.
04:38Nothing works.
04:40Finally, your immune system has to concede.
04:43It will not win this fight.
04:44So it does the next best thing.
04:46Not lose.
04:47Your cells don't know how dangerous these metals and chemicals are,
04:51but they can at least not let them spread around.
04:53So they just stay in place.
04:55They vacuum up all the particles they can fit into their bodies
04:58and surround the larger ones, trapping them in the only prison they can build themselves.
05:04Bit by bit, the ink inside thousands of tiny wounds moves inside millions of immune cells
05:09that freeze in place forever.
05:11On the outside, you don't notice any of this.
05:14Your new tattoo is fresh and the colors vibrant.
05:17Your skin hurts and is irritated and swollen.
05:20But wounds heal, tiny holes close, dead cells are replaced.
05:24Bit by bit, the conveyor belt of death does its job,
05:27shedding dead cells ripe in color, replacing them with fresh and clean ones.
05:32Your tattoo becomes a little less vibrant.
05:34Now the ink is no longer on your skin, but inside it.
05:38But what you're really seeing is millions of your macrophages sitting in your dermis,
05:42patiently holding the ink in place, protecting your body from poison.
05:46Your immune system is why your tattoo is forever.
05:50Actually, nothing is forever.
05:52Over time, your macrophages get old and die, and new ones come in to gobble up the ink and keep it in place.
05:59But sometimes, a tiny bit of ink escapes.
06:01Most of it is recaptured and locked in place, but not always the exact same place.
06:07You notice that as your tattoo fades out a bit and turns less sharp and crisp at its edges.
06:12Some of the ink escapes the tattoo entirely.
06:16It rides fluids flowing from your tissue and spreads around your body.
06:20Another reason why tattoo ink should ideally not be poisoned.
06:24Your immune system also kind of doesn't want you to remove tattoos.
06:28To do that, usually the ink is shot at with lasers, which heats up particles until they break into
06:33smaller chunks, cooking your brave macrophages in the process.
06:36With every round of lasering, more of your tattoo is broken down and carried away by fluids.
06:41But also, every time, new macrophages rush into the tattoo to lock the ink in place.
06:47So, like, hmm, maybe think about it carefully before you get the name of your new bay tattooed.
06:52But you do you.
06:54But if you've got one, you can directly see your immune system protecting you.
06:58This is how much your body loves you, which is kind of sweet.
07:02And while tattoos are probably not that big of a deal for your body if applied correctly,
07:07you now know about the struggle going on inside your skin and the sacrifice of your macrophage
07:12buddies only for you to have that art forever.
07:18To appreciate your amazing immune system, you have to know about it first.
07:22And the same goes for anything going on in our universe.
07:25To help you with that, we've created a series of lessons to take your scientific knowledge to the next level.
07:31Made in collaboration with our friends at Brilliant.org, these lessons let you further
07:35explore the topics in our most popular videos, from rabies and mammalian metabolism to climate
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08:51tools to understand how everything fits together.
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