Physiology of Tattoos
First, a quick history:
Tattooing (permanently marking the skin with pigment) is an ancient tradition, going back thousands of years. Many traditional cultures - from the Picts of Scotland, to the Fulani of Nigeria, the Ainu of Japan, the Maori of New Zealand, the Scythians of Central Asia, and even the culture that Ötzi the Iceman belonged to - used tattoos in either a symbolic way (as an identification or status symbol) or as a form of traditional healing and protection from evil spirits or disease.
Though tattoos have also been used as forms of permanent demarcation of a crime (such as burglary or military desertion), the people of Europe rediscovered a fascination with the artform after many of Captain Cook’s men returned to their home port in 1770, newly tattooed by the Tahitian natives they had encountered in their voyages.
Associated with mariners, lower, and criminal classes for much of the time between the return of Cook’s crew and the 1960s, European gentry went through a phase of great interest in the practice between the 1870s and very early 1900s. As it was both expensive and painful to receive what was considered a high-quality tattoo, it was a sign of wealth and toughness, and in 1898, Harmsworth Magazine estimated that 1 in 5 members of the gentry had at least one tattoo.
Today, though still considered taboo by some, tattoos are not uncommon or (generally) considered a sign of “criminality”. Not that there isn’t discrimination against the tattooed - there definitely is - but it is not what it used to be. Janis Joplin displaying her wristlet tattoo without shame is often considered one of the major turning points for tattoo acceptance in popular culture and Western society. Many people of various ethnic origins have also begun to “reclaim” their heritage and revitalize their previously-suppressed traditional culture, by getting the tattoos that their ancestors wore proudly.
HISTORY LESSON OVER
Tattoos are actually not that complicated! I used to wonder why they didn’t disappear over time (at least not totally), given that every 10 years, every single cell in your body outside of your brain has been replaced at least once.
As it turns out, tattoos create their own little place under your skin. When they’re first applied, the ink is injected into the epidermis and upper dermis, and the body does not like that. Phagocytes flock to the site of the tattoo, and eject the foreign substance from the epidermis - this is what causes the flaking and scabbing over the first couple weeks after a tattoo - and engulf the ink injected into the dermis. As the ink in the dermis is too far down to easily eject, it’s engulfed in a granulation (healing) layer, which turns into connective tissue.
Eventually, the pigment is trapped in fibroblasts, in a discrete layer created between the upper dermis and the epidermis. Fibroblasts, like scar tissue, do not regenerate like regular cells, and tend to stay in one place for an entire lifetime. Some upper dermis layers may form on top of the fibroblasts, leading to fading of the tattoo, but they never completely disappear if they were done in a fashion that created the proper healing conditions.
Laser removal of tattoos currently involves utilizing certain wavelengths of light to shine through the epidermis and break up each pigment shade into particles that are small enough for the body to eject during the normal healing process (initiated by the damage caused by the laser). Previous methods of tattoo removal included dermabrasion, cryobrasion, chemabrasion, and complete excision - all of which either destroyed the epidermis and then the tattoo itself, or which cut out the tattoo entirely. All of those methods tended to produce a significant degree of scar tissue. While some scarring is common with current laser removal, it is nowhere near as extreme as previous methods.
Tattooed: The Sociogenesis of a Body Art. Michael Atkinson, 1971.
"Skin Stories: The Art and Culture of Polynesian Tattoo". Pacific Islanders in Communication for PBS Studios, 2003.
Skin and Bones: Tattoos in the Life of the American Sailor. 2011 Exhibit at Independence Seaport Museum
Tattooed Maori Chief, 1784. From Captain Cook’s first voyage in 1769.
Adult Maori Female, 1890. Portrait by Bohumír Gottfried Lindaur.
"A marriagable girl", 1912. From The Melanesians of British New Guinea, by George Brown.
Kayan (Borneo) Tattoo, 1912. From Customs of the World, photographed by W. H. Furness III.
Mrs. M. Stevens Wagner, Half Length, 1907. One of the first “Tattooed Ladies” who performed as a circus “sideshow freak”.
Ainu woman with traditional tattoo, ca. 1880. “Ainu: Forgotten Indigenous People of Japan.”, 2013.
"Betto, or Groom", ca. 1880. Yamato Japanese man with hair in topknot. Attributed to Adolfo Farsari.
Norman T. Collins, aka Sailor Jerry, ca 1950. Note the heavy Japanese influence in the works of one of the most iconic tattoo artists in history.
Hair! Cross-section diagrams and representations of human scalp hair.
Top diagram: Lengthwise cross-section of human scalp hair follicle (or “bulb”), displaying point of growth
Bottom diagram: Cross-section of human scalp hair, taken from follicle region. Visible hair does not contain the medullary region or fibrous tissue sheath.
Charles Darwin: Androgenic hair [beard] and male-pattern baldness of scalp hair.
Female photographs: Types of scalp hair.
Human scalp hair, as shown here, is two separate structures - a collection of dead filamentous cells, divided into roughly three regions, that extends beyond the epidermis of the scalp, and the “root”, or “bulb”, which can be seen when the hair is pulled out. This is also known as the hair follicle, and is where the hair is created.
There are multiple types of hair on the human, each with its own cellular makeup, but all following basically the same construction pattern. The three primary layers are the cuticle (a few layers of smooth, flat, thin cells, layered like roof shingles), cortex (the roughly rod-shaped keratin cell bundles, just under the cuticle), and the medulla (the innermost disorganized layer that is an open region in the center of the hair - this region is not present in all hair types).
Have you ever noticed that your hair doesn’t all grow at exactly the same rate, and sometimes doesn’t get longer than a certain length? It probably has to do with the length of your growth cycle! Hair growth for each strand on your head can last for 2-7 years, and each stage of growth is happening simultaneously - that is, not every strand is shedding, growing, or resting at the same time. If that were to happen, we’d moult all at once, like birds, and go completely bald every time our hair finished its growth cycle!
Anagen phase: This is the “growth” phase, beginning in the hair follicle, and lasts between two and six years, as determined by genetics. During this phase, the cells in the follicle divide, die, and get pushed out into the visible strand. At any one time, between 80-85% of the follicles on the head are in the anagen phase.
Catagen phase: Catagen is the shortest phase of hair growth; it rarely takes longer than three weeks to complete. This is a transitional phase. When chemical signals from the body signify that it’s time to move past the anagen phase, the follicle begins to shrink and cut the hair shaft off from its blood flow. When the follicle reaches about 1/6 its original size, it is “replenished”, as its generative cells are replaced and it’s not actively creating new hair.
Telogen phase: The resting phase - the hair and follicle remain dormant for between 1 and 4 months, while the follicle regenerates. When the follicle is ready to produce hair again, it pushes the dead hair out of the scalp with the new strand, in the process known as “shedding”.
A Treatise on the Diseases of the Skin. Dr. Henry W. Stelwagon, 1923
A Treatise on the Diseases of the Skin. Dr. Henry W. Stelwagon, 1923
[Young woman modeling: Head, framed in flowing hair]
Charles Darwin by John Collier, 1883.
Ėti︠u︡d golovki by Sergei Mikhailovich Prokudin-Gorskii, c.1905-1915
“They use the pouches while foraging in the same way that hamsters do.”
For reasons I can’t quite comprehend, this illustration comes from a medical textbook entitled “The Anatomy of the Human Peritoneum and Abdominal Cavity, Considered from the Standpoint of Development and Comparative Anatomy,” by George S. Huntington, 1903.