The Skin’s Outer Layer: The Conveyor Belt of Death#

Your skin has a massive job: it’s your biggest organ and gets all the direct contact with the outside world. We’re talking trillions of tiny things like microbes, dirt, insects – all trying to get in. Plus, you’re constantly bumping and scraping your skin just by moving around.

So, your body came up with a clever solution: make the outer layer of your skin a kind of conveyor belt of death.

• The skin you actually see on the surface? That’s all dead stuff.
• The living skin cells start about one millimeter down, in what you could call the skin’s main factory.
• Stem cells down there are always making copies of themselves. These new cells start a journey from the inside, moving outwards.
• Each new bunch pushes the older ones further up.
• As these skin cells grow up, they hook together tightly. They also make tiny bags called Lamellar bodies that squirt out fat. This creates a waterproof layer, sealing any gaps between the cells.
• Then, they dry up, essentially kill themselves, and stick together in solid chunks. This forms a wall of dead bodies that’s constantly moving up.
• Your whole body is covered by up to 50 layers of these dead cells. New cells from below are always replacing them.
• Every single hour, you shed about 200,000,000 dead skin cells, and all the dirt or bacteria stuck to them goes with them.

Trying to tattoo this outer layer wouldn’t work at all. The ink wouldn’t stay because it would just get shed away. To make ink stick, we need to go deeper.

Below the Surface: The Dermis Explodes#

Right below that dead outer layer is the dermis. This is where the magic happens for tattoos.

• The dermis is packed with supportive tissue and different kinds of cells.
• It has tiny blood vessels.
• It contains sensory cells that send messages to your nerve endings.
• It holds the roots of your hairs.
• It has sweat glands to help control your body temperature.
• And, super important for tattoos, it’s loaded with immune cells hanging out, guarding the flesh just below that moving border of dead cells.

This region – the dermis and a bit below – is the target area for your new tattoo.

Alright, you ready? Here’s where things get wild.

The Tattooing Process: A Micro-Scale Disaster#

• Imagine half a dozen huge towers, like skyscrapers compared to a cell, slamming right through those fifty layers of dead cells.
• They plunge deep into the dermis, tearing massive holes in the skin.
• Then, they pull back out, only to smash through the tissue again, about twice every second.
• This action instantly and violently kills tens of thousands of cells. They’re ripped apart or damaged beyond repair.

Now, let’s hope you were smart and picked a good tattoo artist who cleaned their tools and your skin really well. But even with disinfection, you only ever get rid of about 99.9% of all bacteria. Some tough survivors have made it into your flesh.

Your immune system? To say it’s not happy is an understatement!

The Immune System’s Alarm: Macrophages Respond#

All this death and destruction wakes up hundreds of thousands of immune cells called Macrophages in your dermis. They rush towards the open wounds to protect you.

• Right away, they start trying to kill any bacteria they find.
• They release chemicals that are basically calls for backup.
• They tell your blood vessels to open up, which is why your dermis starts to swell up with fluid.

But even worse than the wounds and the few invading bacteria is the massive wave of chemicals flooding your tissue.

The Challenge of Tattoo Ink#

Tattoo ink can be made from all sorts of stuff – hundreds of different substances. Some of them might even be toxic or cause cancer. A lot of inks use heavy metals like lead, nickel, or chromium, mixed into distilled water.

The area where the tattooing happened is now a chaotic mess:

• Pieces of dead cells.
• A few panicked bacteria.
• Blood and other bodily fluids.
• Platelet cells trying to patch up the holes.
• More and more fresh immune cells arriving.
• And the flood of tattoo ink.

On the tiny scale of your cells, the clumps of ink particles are huge. If you were the size of a cell, the ink particles could range from being as big as large dogs to small office buildings.

Your immune system has one main job: find anything that isn’t part of you and smash it until it’s gone. The Macrophages are trying their best to do this.

• Like tiny octopuses, they stretch out arm-like parts and start pulling the ink particles inside themselves.
• Normally, when a Macrophage eats an enemy, it drowns it in acid to break it down.
• But this doesn’t work on the ink! They try and try, but nothing happens; the ink particles don’t react at all.

And that’s just the particles small enough for a Macrophage to even eat! The bigger chunks of ink are now surrounded by thousands of your structural skin cells and other Macrophages. These cells are nibbling on the ink, bathing it in acid and attack chemicals, trying to destroy it. But the ink isn’t moving or changing even a tiny bit. Nothing they do works!

The Immune System’s Solution: Imprisonment#

Finally, your immune system has to admit defeat. It can’t win this fight by destroying the ink, so it does the next best thing: it refuses to lose.

Your cells might not know exactly how dangerous these metals and chemicals are, but they know they can stop them from spreading around your body. So, they decide to just stay put.

• They suck up all the ink particles they can fit inside their own bodies.
• They surround the larger pieces, trapping them.
• The only prison they can build for the ink is… themselves.

Little by little, the ink that was scattered in thousands of tiny wounds gets pulled inside millions of immune cells. And these cells freeze in place, holding the ink forever.

Your Tattoo’s Appearance: Inside the Immune System#

On the outside, you probably don’t notice any of this cellular battle. Your new tattoo looks fresh, the colors are bright. Your skin hurts, it’s irritated and swollen – totally normal.

But wounds heal. The tiny holes close up. Dead cells are replaced. Bit by bit, the conveyor belt of death does its job, shedding the dead skin cells that might have had some color on them initially, and replacing them with fresh, clean ones.

Your tattoo starts to look a little less bright on the very surface. Why? Because the ink isn’t sitting on your skin anymore; it’s locked away inside it.

What you’re seeing is actually millions of your Macrophages, sitting patiently in your dermis, holding the ink in place, protecting your body from potentially harmful substances.

Your immune system is the reason your tattoo is permanent.

Is Anything Truly Forever? Fading and Removal#

Okay, so “forever” isn’t exactly true. Over time, your Macrophages get old and die. When that happens, new Macrophages come along to gobble up the ink particles released by the dying cells and lock them away again. Most of the time, they put the ink back in pretty much the same spot.

But sometimes, a tiny bit of ink escapes during this process. Most of this escaped ink is recaptured and locked up, but not always in the exact same place. This is what you see as your tattoo fades a bit and the edges become a little less sharp and crisp over the years.

Some of the ink actually escapes the tattoo area completely. It gets carried away by the fluids flowing through your tissue and can spread around your body. This is another good reason why tattoo ink really, really shouldn’t be poisonous!

Your immune system also makes tattoo removal a bit tricky.

• Removal usually involves shooting the ink with lasers.
• The lasers heat up the ink particles, causing them to break into smaller pieces.
• This process can actually cook your brave Macrophages holding the ink!
• With each laser session, more of your tattoo ink is broken down into smaller bits and carried away by bodily fluids.
• But, every single time, new Macrophages rush into the area to grab the ink particles and lock them up again.

So, yeah, maybe think extra carefully before getting a spur-of-the-moment tattoo of your new crush’s name! But hey, you do you. If you do have one, you can directly see your immune system working hard to protect you.

It’s kind of sweet, right? It shows just how much your body loves you by putting in all this effort. While tattoos, if done properly, probably aren’t a major health crisis for your body, you now know about the intense struggle happening inside your skin and the sacrifice of your Macrophage buddies, all so you can have that art permanently.

Learn More About Your Amazing Body and Universe#

To really appreciate how cool your immune system is, you need to understand it. And the same goes for everything else amazing happening in our universe!

To help you explore this stuff, we’ve teamed up with our friends at Brilliant.org to create a series of lessons designed to boost your science knowledge.

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