Secret of tattoos’ longevity
According to a 2018 study, 18%, or about one in five of the French population is tattooed. The popularity of tattoos continues to grow year after year, and they are now perceived as works of art. But what happens once the needle has pierced the skin? Where do the ink pigments go? Why does a tattoo not fade over time? There is an explanation for everything.
Skin is the largest and heaviest organ in the human body, with a surface area of about 2 m2 for an adult. It has many physiological roles, notably the maintenance of body temperature, the perception of touch, immunity, protection from the external environment and many other. It is composed of three different layers,giving it an onion-like structure.. In contact with the outside world is the epidermis, which is renewed every few weeks. The epidermis is made up of sub-layers of cells that are at different stages of life, from the deepest (stratum basale) to the surface (stratum corneum). In the stratum basale, the cells are alive and replenishing themselves daily. They will divide and some will move to the upper layer (stratum spinosum). As they advance through layers they lose a little more of their function each time, until they reach the stratum corneum as dead cells. It's a bit like a bowl of cereal filled with milk. Your spoon will pick up the cereal on the surface of the milk (the cells of the stratum corneum will break off with the contact of the environment) and the cereal that was underneath will rise to the surface (the cells of the stratum basale will migrate to the upper layers).
Epidermis structure scheme
(Source : http://orogoldschool.com/web/cold-weather-harmful-skin/attachment/orogold-is-cold-weather-harmful-for-your-skin-structure-epidermis/)
Next comes the dermis, which is what we call connective tissue. It is a complex tissue, which, unlike the epidermis, is not composed solely of cells, rather it is a gelatinous tissue composed of different types of cells (fibroblasts and immune cells called macrophages), fibers (such as collagen) and other substances (such as hyaluronic acid). It is also a tissue rich in blood vessels which help to nourish the epidermal cell layer.
Finally, the lowest layer of the skin is the hypodermis, which is a connective tissue as well. It provides the link between the skin and the muscles below. It also serves as a nutrient reserve (stock of adipose cells, which contain fat) for the entire skin.
(source : https://natstory-cosmetiques.fr/le-collagene/)
Ink under the skin
For a tattoo to last, the ink must be deposited in a skin layer where it can last. As the epidermis renews itself in a few weeks, it is not this area that is tattooed. In fact, the needle will pierce to the dermis to deposit the tattoo ink, 1 or 2 millimetres below the surface of the skin. When the needle withdraws, some pigments will scatter in the different layers of the epidermis, which will give the tattoo a "bright" color in the first days. These excess pigments will disappear as the skin is renewed.
Ink injection under the skin
(source : https://www.tedxmilehigh.com/rise-smart-tattoos/)
It is because the needle pierces the very blood vessel-rich dermis that the tattoos bleed at the beginning, during cicatrization time.
Safeguarding the tattoo
For a long time, it was thought that the tattoo ink was stored between the cells of the dermis, in the gelatinous tissue. Afterwards it was learned that when the ink was injected into the skin, it was stored in two different cell types.
Most of the pigment will be phagocytosed by macrophages (immune system cells) in the dermis. Phagocytosis consists of ingestion of larger or smaller elements by the cells. Usually, macrophages phagocytose viruses or bacteria during an infection and digest them. But in this case, the macrophages that have eaten the tattoo pigments will then remain in their original location in the dermis, rather than digest the pigments.
Some of these macrophages will migrate to the lymph nodes (the stock of immune soldiers) and it has even been observed in some people with many tattoos that the nodes are colored because so many macrophages have brought the pigment back .
For a long time, it was thought that these cells were immortalized because the ink did not fade over time. In fact, when a macrophage dies, it will release the pigments from the tattoo into the dermis, which will be eaten again by another macrophage, and so on for the rest of the person's life.
Pigment storage cycle by macrophages
(source : https://www.scienceabc.com/eyeopeners/why-do-tattoos-last-forever-if-skin-constantly-sheds.html)
It is assumed that therefore tattoos eventually spread and lose their detail, as the new macrophages would not be positioned in the same places as the previous ones. For this reason, some people touch up after a few years.
Example of a tattoo after several years
(source : https://hitek.fr/42/avant-apres-tatouages-usure_4948)
Some of these pigments will be stored in another type of cell: the fibroblasts. These cells secrete all the components of the gelatinous tissue. Like macrophages, fibroblasts phagocytose the tattoo pigments and store them until they die. But unlike macrophages, when they die and the pigments are released, they will not be eaten again by young fibroblasts. They will be eaten by young macrophages.
Tattoos and sun don't mix
The displacement of macrophages is not the only explanation for the spreading of tattoo ink. Many external elements can contribute to this, in particular the UV spectrum of the sun. There are 2 types of UV light we need to worry about: UVA and UVB.
UVB does not penetrate further than the epidermis and is responsible for tanning (and therefore sunburns). It can cause skin burns but is not directly responsible for the alteration of a tattoo.
The responsible ones are the UVA rays that penetrate to the dermis. UVA will not cause burns, they are painless. However, they will cause a lot of damage to the tissues, such as skin loosening, allergies and DNA alterations that can lead to cancer. These UVs will also degrade the ink molecules and the debris will then be eliminated by the body. This is an effect that can be compared to the effects of lasers, which can be used to remove the pigments of a person's skin.
That's why if you value your tattoos, protect them!
1. S. Garcovich et al. Lichenoid red tattoo reaction: histological and immunological perspectives. European Journal of Dermatology. 2012.
2. H. Strandt et al. Macrophages and fibroblasts differencially contributes to tattoo stability. Karger dermatology. 2021.
3. C.A. Grant et al. Tattoo ink nanoparticles in skin tissue and fibroblasts. Beilstein J Nanotechnol. 2015.
4. B. Dreno. Tatouage et réaction sarcoïdosique. Elsevier. 2020.
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