How Laser Tattoo Removal Works - Smarter Every Day 123

Hey it's me Destin

Welcome back to Smarter Every Day.

So in the last video we talked about what it

was like to get a tattoo in slow motion.

But this time we're gonna talk about the

removal process. It's way more complicated.

It involves physics like thermodynamics,

optics, even biology and chemistry are involved.

So today on Smarter Every Day we're gonna go

get some ink and then go to a plastic surgeon

and see if we can get it removed. Check it out.

(Destin) Can I steal some ink?

- Yeah.

- [laughs] Thanks. Yes.

So before we talk about how to get the ink

out of the body let's talk about what exactly

you're putting into it.

Most people don't realize this but the bright

colors in tattoo inks are actually created from

compounds that mostly use heavy metals.

I know, that's kind of crazy right?

I mean, you go to all these great lengths at a

tattoo parlor to have a sterile field so no

pathogens transfer, but if you think about it,

they're essentially making a very clean way

for you to inject heavy metals into your body.

It's kind of crazy if you think about it.

Anyway, let's go talk to a smart guy.

OK, so we we want to know how to remove

a tattoo with a laser so we're here with Dr Lappert,

plastic surgeon.

- Pleasure.

- Yes, so I have some questions.

You've got some big machines beside you here,

- Sure.

- I'm assuming these are lasers?

- Yes they are.

This one over here is an ultra short pulse laser

that we use for the tattoo removal.

- We're talking nanosecond level?

- No. Even shorter than that.

- Really.

- Picosecond level.

- Really.

- So a decimal point, eleven zeroes, and then put a digit

in there somewhere and you've got picosecond time scale.

So this is.. this one here is an alexandrite laser,

and alexandrite lasers are sort of tuneable within a

certain narrow frequency range but we're gonna

be operating at about 755 nanometers with this thing.

- Oh wow. So that's just in the infrared right?

- Right.

- Alright before we start zapping stuff I want to

know exactly what it is we're going to zap.

I've got a little drop of tattoo ink here and

I'm gonna put it on this slide and place

it under my microscope in hopes that we can

see those metals.

When we zoom in you can see these little bitty

ink particles moving around, and then there's

these much bigger chunks.

Take just a second before we go further

and remember what that slow motion tattooing

I recorded in the last episode looked like.


Alright, now that we know what the ink looks

like mechanically, we can draw a better picture

of what's happening.

Multiple needles are puncturing your skin

and dragging both big and little ink particles

down through the epidermis into the dermis.

- From the moment the tattoo is placed however

your body's trying to get rid of it.

Your body recognizes that it's foreign material

as if you got a sliver under your skin.

So your immune system is coming over

looking at this stuff going "hey this

doesn't belong here".

White blood cells come in to remove the pigment.

Now the white blood cell is a very small little cell

whereas the pigment granule is a relatively large

structure if you looked at it under the microscope.

That white blood cell actually comes over and

tries to engulf the pigment granule, and because

the white cell is so small and the pigment granule is

so big, that munching away is a very difficult thing.

It's like trying to take a bite out of an elephant.

- Alright, so this is about to get weird but I have to do this.

I want to know how big my blood cells are relative

to the ink particles.

So obviously we have to prick my finger and get some

blood and put it in there with the ink.

Alright here we go and we put the microscope

slide in and it is more awesome than I

thought it would be.

It is, look at it.

So we've got blood cells interacting with ink

so we can see the relative scale of the two right?

So we've got these little bitty ink particles

that are smaller than the blood cells

and we have the larger ink particles that

are larger than the blood cells.

That means the small ones can be drug away

by the phagocytes or the white blood cells,

but the larger ones can't.

That's why tattoos are permanent,

but that's also why they fade right,

because part of the ink is drug away

but part of the ink stays.

That's awesome.

That's like so awesome.

- If you look at a freshly placed tattoo,

it looks very sharp, it has very clean edges,

very clear colors, very crisp.

- Right.

- If you look at a tattoo on a retired master gunnery sergeant

from the marine corps, that tattoo's starting

to look faded.

- Right.

- Because what's happening is that pigment is being eaten

by those white blood cells and carried through

the lymphatics of the skin, because it's headed for

your liver, and that process has been going on

in the gunnery sergeant for 35-40 years.

- I find that hilarious that you're picking on gunnys

because I know a couple of gunnys.

- Well I'm retired navy.

- Oh so you're allowed to say it.

- Oh yeah I served the marine corps for years.

- OK good.

- The problem is that the relative size of the

white blood cell and the pigment granule,

big pigment granule, little white blood cell.

So what the laser does, is if you have the

right type of laser when you hit it with a pulse

of light, hit the pigment granule with a pulse of light,

that pigment granule will shatter, OK.

And so as you shatter the pigment granules

you're making them smaller and more edible.

- Really.

- So you're accelerating the speed with which

the white blood cells, and the efficiency with

which the white blood cells can remove the pigment.

- So they're trying to take it to the liver.

- Correct. That's the way out.

- So you're gonna zap the ink with this laser.

- Correct.

- And then the white blood cells are gonna go

grab the broken up ink particles and

take it to the liver.

- That is correct. Through the lymphatic

channels of the skin, into the larger lymph

channels deeper down, and ultimately

through the liver for cleaning up and excretion.

- So how does an optical energy source

shatter a mechanical ink particle?

Think about this.

Let's say we have a heat lamp, and we

turn it on and we shine radiation energy

on one side of an ink particle.

What's gonna happen is it's gonna heat up

that side and then the heat transfer

coefficient is gonna cause the entire ink particle

to heat up from this side towards this side right?

There's gonna be a heat gradient.

What if we had a really really really hot heating lamp

and it was very very fast.

Assuming the laser and the ink are the right color,

this laser will shine on one side of the particle

and heat it up so fast that only that side grows

due to thermal expansion.

The other side however doesn't have time to catch up,

so it's still cool which causes huge internal

stresses which rip apart the particle.

That's why it's a time game.

The faster you can heat up one side relative

to the other, the more likely you can rip apart the ink.

The more exposure time, the more tissue you affect.

- Correct.

- But the smaller exposure time, the more

localized if you hit the right chromophore.

- Correct.

- I feel like I know the big words now. [laugh]

It's awesome.

So once it's shattered, the white blood cells

are gonna come get those little broken

particles of ink, take it to the lymph nodes

then dump it off to the liver and then you're

eventually gonna poop out your tattoo.

That's how it works.

- The aiming beam is a helium neon laser,

very low energy but it allows me to see where the

actual pulse is gonna go.

Alright you ready?

- I am now ready.

- OK here we go.


I'm just gonna keep treating while you...

You can see what I mean about the

frosting right?

- I do.

- How it elevates the top layer of skin there.

- So there you go.

That white effect that you're seeing

is called frosting, and it only lasts for

just a few seconds. It's basically a shock

wave that's happening at the particle level.

Dr Lappert says that depending on the color

this could take just a few treatments

before the body can fully process the ink.

Alright so I hope the take away from this

episode was, if you're gonna get a tattoo,

know exactly what you're doing.

What are you getting tattooed into your body,

meaning chemically what are they putting

into you, and also what is the design.

Think it through because it's a lot harder

to get a tattoo off than it is to put it on.

Think about it.

Alright, so if you enjoyed all the sciences

in this episode, optics, thermodynamics,

chemistry. You will enjoy this audio book

I'm about to recommend.

Many of you know that Audible.com

sponsor Smarter Every Day, but you

just need to listen to this book, I don't

care how you do it. If you go to

audible.com/smarter you can get

this book for free. It's called

The Martian by Andy Weir.

This book is incredible.

You just need to listen to it.

I would love to be the guy that

introduced you to it, but you just

need to experience it on your own

because he's stranded on mars and he

has to MacGyver himself off.

Think about that.

We're talking like radio electronics,

orbital mechanics, rocket propulsion,

chemistry, biochemistry, thermo.

It's awesome!

Anyway, The Martian by Andy Weir,

I really really really enjoyed it.

If you liked this episode you're

gonna like it too. So there you go.

Please experience that, and you can

thank me later. However don't do

what I did and start the book with your

two year old in the car because there's

a little bit of cussing. I apologize about that

but I think it's worth it.

Anyway, audible.com/smarter.

I hope you enjoyed this episode and it

earned your subscription.

If not, thank you anyway for watching,

I really appreciate that.

I'm Destin, you're getting Smarter Every Day.

Have a good one.

If somebody's going to get a tattoo removed,

what are the questions they need to ask,

just briefly.

- How long will it take me to drive to Dr Lappert's office.

- [laugh]

We will leave it with that. There's your doctor..

Dr Lappert, plastic surgeon. There you go.

You are something else man.