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 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 tunable 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. [music]
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, hitting 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. [clicking] 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 takeaway 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 sponsors 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.