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Humans have been tattooing themselves for thousands of years, for spiritual, cultural, or personal reasons.
Long before we were covering ourselves in ironic stick'n'pokes, butterfly tramp stamps, or full blackout tattoos, humans were marking their bodies with permanent ink.
But while history can tell us much about the culture of tattooing, we still don't know much about how the practice affects our health.
Introducing tattoo pigment into the skin triggers an immune response, and that ink obviously sticks around – though it doesn't always stay put.
Research shows that particles of tattoo ink can enter the lymphatic system and build up in the lymph nodes.
Lymph nodes are key hubs of our bodies' immune activity. Full of white blood cells, lymph fluid is filtered through them to clean out any debris it's collected on the way around your body. That includes misbehaving cells (i.e. cancer), bacteria, viruses, and foreign substances such as tattoo ink.
Rapper MGK recently found this out the hard way by rushing a massive blackwork piece that covers much of his torso, including the area of the lymph nodes around his armpits and shoulders. He says the process turned his surrounding skin yellow and made him "really sick."
Even without traveling through the body, tattoo pigment 'sets off' the immune system. Pigment enters cells in the dermis, the middle layer of skin, and is swiftly recognized as a foreign substance. The body sends its 'army' of immune cells, but the pigment particles are too large for these cells to remove.
That's what makes tattoos permanent, but it also sets up the body for a lifelong battle against an impossible-to-remove invader.
What helps make tattoos so permanent is that modern inks are made of a complex cocktail of chemicals.
"They contain pigments that give color, liquid carriers that help distribute the ink, preservatives to prevent microbial growth, and small amounts of impurities," medical microbiologist Manal Mohammed explained in an article for The Conversation.
"Many pigments currently in use were originally developed for industrial applications such as car paint, plastics, and printer toner, rather than for injection into human skin."
Researchers have detected trace quantities of heavy metals in tattoo inks, including nickel, cobalt, chromium, and, on rare occasions, lead. Accumulated at high levels, heavy metals can be toxic, causing serious health problems such as internal organ damage, neurotoxicity, and increased cancer risk.
In some cases, these heavy metals triggered allergic reactions and immune sensitivity in the person receiving the tattoo.
We'll never forget the harrowing story of a Polish man whose immune response to a red ink tattoo included losing the ability to sweat, shedding all his body hair, and developing vitiligo, a skin-lightening condition.
"Colored inks, particularly red, yellow, and orange, are more frequently associated with allergic reactions and chronic inflammation," Mohammed explained.
"Red ink is particularly associated with persistent itching, swelling, and granulomas… small inflammatory nodules that form when the immune system attempts to isolate material it cannot remove."
The allergic reactions and chronic inflammation triggered by colored inks are partly due to the metal salts and azo pigments.
Azo pigments are organic compounds that are included in tattoo ink for their vibrant colors. They're used in textiles and plastics for that same reason.
But these pigments can break down into aromatic amines when exposed to certain forms of radiation: the kind your skin might cop if you spend too long in the sun, for instance, or if you decide the tattoo was a mistake and go in for laser removal.
And that's concerning, because lab studies have linked aromatic amines to cancer and genetic damage.
Tattoo pigments – especially black ones – can also include polycyclic aromatic hydrocarbons, which are found in soot, vehicle exhaust, and charred food. Many of these hydrocarbons are also classed as carcinogenic.
So far, there has been no strong evidence in humans that links tattoos to cancer – but lab and animal studies indicate there may be risks.
One observational study published late last year also found tattooed people had a 29 percent higher risk of melanoma (a kind of skin cancer), though other recent studies haven't found a link.
The immune responses that tattoos can trigger should also be taken into serious consideration before booking in for fresh ink.
"While current evidence does not suggest widespread danger, growing research highlights important unanswered questions about toxicity, immune effects and long-term health," Mohammed wrote in The Conversation.
"Chronic inflammation has been linked to tissue damage and increased disease risk. For people with autoimmune conditions or weakened immune systems, tattoos may pose additional concerns."
There's also the risk of infection involved in putting any foreign matter, including the tattoo needle, into your skin.
The tattooing process breaks the skin barrier, which is one of your body's important defenses against infections such as Staphylococcus aureus, hepatitis B and C, and, in rare atypical mycobacterial infections.
The tattoo industry is largely unregulated in many countries, so it pays to be aware of the risks and take things slow if you decide to get inked.
Related: Study Uncovers Hidden Ingredients in 83% of Tattoo Inks, Raising Concerns
It's important to talk to your tattoo artist about what inks they use and what hygiene practices they follow. And if you have any history of immune problems, talk to a doctor before going ahead.
"Tattoos remain a powerful form of self-expression, but they also represent lifelong chemical exposure," Mohammed concluded.
"As tattooing continues to rise worldwide, the case for better regulation, transparency, and sustained scientific investigation becomes increasingly difficult to ignore."
This article was fact-checked by Rebecca Dyer and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
