Tattoos
Tattoos
by Jasmine Chan
INTRODUCTION TO TATTOOS
Tattoos are a form of human modification, a type of design that is permanent on the skin by inserting a type of ink or dye using needles. Tattoos have been part of human culture for centuries. It is considered a form of body art, where people can express themselves with designs permanently on their bodies. [1]
INTRODUCTION TO THE HUMAN SKIN
Before I start addressing how tattoos work, I need to talk about the human skin to understand its role in the permanence of tattoos.
Skin is the largest organ in humans and it is part of the integumentary system. This integumentary system protects the inside of the body from the environment. [2] The skin is made of three layers: the epidermis, the dermis and the hypodermis. [3]
The epidermis is the top layer of the skin. It is the layer where dead cells are continually shed. New cells form from the bottom of the epidermis and rise to the skin surface to replace the old cells. It also contains cells with melanocytes, which contain melanin - a type of pigment which gives rise to each person’s skin colour. It also contains keratin which provides toughness and strength to provide toughness and strength to the skin. [2, 4]
The dermis is the middle layer of the skin, underneath the epidermis. It is a layer that contains blood vessels and nerves. Sweat glands, oil glands and hair follicles are also found here. The dermis is mostly made of collagen, a protein that makes the skin flexible and strong. As the dermis has a lot of nerves, it contains a lot of receptors that allow us to feel and touch. It is also the layer that contains lymphatic vessels which help to fight off an infection by initiating an immune response. [2]
The subcutis, also known as the hypodermis is the subcutaneous fat layer that helps to insulate the body by storing fat to provide padding to internal organs such as muscle and bones. [2,4]
INTRODUCTION TO TATTOOS
Fig.3 Cross-Sectional Diagram of the Layers of Skin and How Tattoos Work
Tattoos work by injecting a bundle of tiny needles containing a solution containing pigments into the skin, through the epidermis to the dermis at a frequency of 50-3000 punctures a minute. [5, 6] This process is known as permanent inflammation. [7] Once the needle is inserted into the dermis, the pigment inserted would start an immune response. Just like when any foreign substance enters the body, this triggers macrophages to go towards the site of damage - the area where the needle is inserted. [5] Phagocytosis then occurs where phagocytes, a type of macrophage, engulfs the larger inorganic pigments in the tattoo solution. Using their pseudopodia made from their cell membrane, it wraps around the pigments and traps them into a phagosome (a vesicle). A lysosome containing enzymes known as lysozymes are able to move towards the phagosome and fuses with the membrane of the phagosome. [8] As the foreign item is pigments instead of phagocytes such as bacteria, the lysozymes have no effect on the pigment at all which means that the pigment would remain in the phagocyte. [5] Smaller inorganic pigments in the tattoo solution are then passively transported and deposited in the lymph nodes. [6, 9]
If the needle is inserted incorrectly, such as not into the dermis, there can be consequences. If the pigment is injected into the epidermis instead of the dermis, since the epidermis is not the site of lymphatic vessels, an immune response will not occur. This can create a non-permanent design as overtime, the cells containing the pigment would shed. [5, 6] If the pigment is injected into the subcutis instead of the dermis, the pigment can spread through the underlying layers of the skin, making the design not defined and crisp. [5]
HOW DO TATTOOS REMAIN ITS PERMANENCE?
The ink would remain the sinusoids of the draining lymph nodes as there is no way of removal of these pigments out of the body. [6, 9] However, for the macrophages, the process is not as easy as remaining in the cell. Overtime, macrophages die. This means that the pigment cannot just remain in the cell forever. When the macrophage containing the pigment dies, the pigment is released and exposed to the dermis again. Another macrophage would engulf the pigment and undergo phagocytosis again. The release and recapture cycle continues, causes tattoos to be permanent. [5, 10]
TATTOO REMOVAL
There is one specific way to remove tattoos from the body, which is known as laser removal. These lasers work by a process known as selective photothermolysis. [11, 12] Selective photothermolysis is a technique using pulses of light to produce heat damage to the directed surface - in this case, skin with the tattoo pigments. [13] The light used in the laser has a specific wavelength and heats the targetted tissue to destroy the tissue. The cells destroyed as they absorb the light energy. This technique ensures that the damage is localised, and prevents surrounding tissues from being damaged. [12]
Black tattoos are the easiest to remove with this process as it is able to absorb all wavelengths of light. Hence, coloured tattoos are a lot tricker as they need to use lasers that release specific wavelengths in order to be removed. Tattoo removals is a long process and may take more than 5 sessions to completely remove the tattoo on the skin. [11]
This technique works as the specific wavelengths can target tattoo pigments at its chromophores - a group of atoms and electrons that forms an organic molecule which causes it to be coloured. [14, 15] The target chromophore is heated quickly before it can cool down again. As tattoo particles are incredibly fine and small, rapid pulses with high heat are required to prevent the particles from cooling down quickly. [14] For maximum destruction of these particles, the duration of the pulses must be shorter than the time that is required for the chromophore to lose 50% of its heat or be shorter than the thermal relaxation time (how quickly a substance loses heat) of the tattoo. [14, 16] If the duration is longer, the target chromophore does not get damaged. Instead, this energy is dissipated to the surrounding tissues which is not ideal during a tattoo removal. [17]
BIBLIOGRAPHY
[1] “Safety of Tattoos and Permanent Make-up (PMU).” Green Facts, www.greenfacts.org/en/safety-tattoos/l-2/index.htm.
[2] Zimmermann, Kim Ann. “Skin: The Human Body's Largest Organ.” LiveScience, 22 Oct. 2018, www.livescience.com/27115-skin-facts-diseases-conditions.html.
[3] “Skin Deep Science – How Do Tattoos Work?” Australia's Science Channel, 12 Sept. 2017, australiascience.tv/skin-deep-science-how-do-tattoos-work/.
[4] “How Does Skin Work?” NCBI, U.S. National Library of Medicine, 11 Apr. 2019, www.ncbi.nlm.nih.gov/books/NBK279255/.
[5] Bryon-Dodd, Kimberley. “Inking the Immune System: How Macrophages Make Tattoos Last.” Bio-Rad, 4 Apr. 2018, www.bio-rad-antibodies.com/blog/how-macrophages-make-tattoos-last.html.
[6] Aguirre, Claudia. “What Makes Tattoos Permanent?” TED, ed.ted.com/lessons/what-makes-tattoos-permanent-claudia-aguirre.
[7] “Why Tattoos Are Permanent - It's Not What You Think.” ZME Science, 1 Feb. 2021, www.zmescience.com/science/biology/why-tattoos-are-permanent-0554/.
[8] Cooper, Geoffrey M. “Lysosomes.” NCBI, U.S. National Library of Medicine, 1 Jan. 1970, www.ncbi.nlm.nih.gov/books/NBK9953/.
[9] “Synchrotron-Based ν-XRF Mapping and μ-FTIR Microscopy Enable to Look into the Fate and Effects of Tattoo Pigments in Human Skin.” Nature News, Nature Publishing Group, 12 Sept. 2017, www.nature.com/articles/s41598-017-11721-z.
[10] “Unveiling Skin Macrophage Dynamics Explains Both Tattoo Persistence and Strenuous Removal.” Journal of Experimental Medicine, 2 Apr. 2018, rupress.org/jem/article/215/4/1115/42419/Unveiling-skin-macrophage-dynamics-explains-both.
[11] “The Science Behind Laser Tattoo Removal.” The Science Explorer, thescienceexplorer.com/brain-and-body/science-behind-laser-tattoo-removal.
[12] Kita, Natalie. “Selective Photothermolysis Is Used to Treat Different Conditions.” Verywell Health, 27 Jan. 2020, www.verywellhealth.com/what-is-selective-photothermolysis-2710175.
[13] “Photothermolysis.” The Free Dictionary, medical-dictionary.thefreedictionary.com/photothermolysis.
[14] Henley, Jill K. “Laser Tattoo Removal.” NCBI, U.S. National Library of Medicine, 15 Feb. 2021, www.ncbi.nlm.nih.gov/books/NBK442007/.
[15] “Chromophore.” Encyclopædia Britannica, 6 Dec. 2011, www.britannica.com/science/chromophore.
[16] Murphy, Mike. “More on Thermal Relaxation Times.” Mike Murphy's Blog, 14 Dec. 2017, mikemurphyblog.com/2017/12/14/more-on-thermal-relaxation-times/.
[17] Patil, Uddhav A., and Lakshyajit D. Dhami. “Overview of Lasers.” NCBI, U.S. National Library of Medicine, Oct. 2008, www.ncbi.nlm.nih.gov/pmc/articles/PMC2825126/.
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