Researchers found that immune cells called macrophages — which normally capture bacteria and viruses — absorbed the ink. However, instead of breaking down the pigment, these cells died.
Published Dec 10, 2025 | 7:00 AM ⚊ Updated Dec 10, 2025 | 7:02 AM
Tattoo Artist making a tattoo on a shoulder in tattoo studio. (iStock)
Synopsis: Scientists at the Institute for Research in Biomedicine in Switzerland spent seven years tracking what happens to tattoo ink after it enters the skin, revealing that the ink does not stay put. Researchers found that immune cells called macrophages — which normally capture bacteria and viruses — absorbed the ink. However, instead of breaking down the pigment, these cells died.
A person walks into a tattoo parlour, sits through hours of needlework, and admires the fresh design. What they don’t see: Millions of pigment particles already moving through their body, travelling towards lymph nodes where they will remain for months, changing how the immune system functions.
Scientists at the Institute for Research in Biomedicine in Switzerland spent seven years tracking what happens to tattoo ink after it enters the skin. Their findings, published in the Proceedings of the National Academy of Sciences(PNAS), reveal that ink does not stay put.
“When you tattoo your skin, you also ‘tattoo’ your immune system,” the Institute said in its statement.
The study tested black, red, and green inks on mice and examined tissue from humans with tattoos. Within ten minutes of tattooing, ink particles appeared in lymphatic vessels — the body’s drainage system. Within 24 hours, large quantities had accumulated in lymph nodes, the organs that filter infections.
Two months later, the amount of pigment in these nodes had increased. Black and red inks travelled furthest, reaching multiple lymph nodes. The same patterns appeared in human tissue samples.
Lymph nodes function like checkpoints, screening everything that flows through the body. Researchers found that immune cells called macrophages — which normally capture bacteria and viruses — absorbed the ink. However, instead of breaking down the pigment, these cells died.
The team isolated macrophages and exposed them to different ink concentrations. Red and black pigments triggered cell death within 12 hours. When researchers counted immune cells in tattooed mice, macrophage numbers spiked within six hours, then crashed. New cells arrived, swallowed pigment, and died, creating a brutal cycle.
“The interaction of ink pigment with macrophages depends on their physicochemical characteristics and can lead to cytotoxic events, including cell viability perturbation via apoptosis or necrosis, oxidative stress, and reactive oxygen species generation,” the researchers noted.
Human cells grown from blood samples showed identical responses. All three ink colours killed cells, though timing varied.
This matters because macrophages in lymph nodes filter fluid constantly, capturing viruses and bacteria before they reach the bloodstream. If these cells are dying from ink exposure, they cannot stop pathogens.
The death of immune cells triggers inflammation — a response that summons reinforcements and increases blood flow. Researchers collected fluid from tattooed mice and measured chemical signals over a period of 10 days.
Some signals spiked within hours, then returned to normal. But others, including IL-1α, a danger signal released by damaged cells, stayed elevated for two months.
Blood samples revealed inflammation spread throughout the body. At the two-month mark, lymph nodes remained enlarged. The total number of immune cells exceeded normal levels.
“The elevated levels of the alarmin IL-1α in the draining LN were maintained during the first two months following tattooing with black ink. Interestingly, we have previously associated the elevated levels of this cytokine with the initiation of melanoma metastasis in the LN,” the study noted.
A Swedish study of nearly 12,000 participants found that people with tattoos faced a 21 percent higher risk of lymphoma — cancer of the lymphatic system.
During the Covid-19 pandemic, questions emerged about whether tattoos might interfere with vaccination. The Swiss study provided the first experimental evidence.
Researchers tattooed mice, then administered the Pfizer-BioNTech mRNA vaccine either two days or two months later. Tattooed animals produced significantly less antibody against the coronavirus spike protein. The effect persisted whether the tattoo was fresh or old.
Macrophages in tattooed mice expressed lower levels of spike protein—the substance that trains the immune system to recognise coronavirus. When the vaccine was injected into the opposite leg from the tattoo, antibody production returned to normal.
Human cells confirmed the finding. Macrophages from six healthy donors were exposed to tattoo ink, then mixed with the Covid-19 vaccine. All three ink colours reduced antibody production.
However, not all vaccines responded the same way. When researchers tested an inactivated influenza vaccine, tattooed mice produced more antibodies, not fewer. Black and red inks increased immune responses.
“Tattoo-induced local inflammation can act as an adjuvant-like stimulus, enhancing vaccine responses, similar to aluminium salts activating the NLRP3 inflammasome,” the researchers explained.
Dr S Madhavi, a Hyderabad-based General Physician, called the vaccine findings the study’s most striking result. “An unpredictable vaccine response means some vaccines may become less effective on tattooed individuals. Local inflammation from tattoos can interfere with antigen processing. Doctors already advise avoiding fresh tattoos before vaccination—this study explains why.”
Earlier this year, Karnataka’s Food Safety Department had tested tattoo ink samples and found 22 heavy metals, including selenium, chromium, platinum, and arsenic, as well as microorganisms that could cause infections.
“Unlike cosmetics, which undergo strict safety testing, tattoo inks currently exist in a legal grey area in India, with no quality control, safety standards, or government oversight,” officials noted in a letter to the Union Health Minister.
The letter stated: “The officials have taken samples of tattoo inks from the market and subjected them for testing and the reports are alarming. The tattoo inks showed positive for around 22 metals in ppm levels and residual solvents.”
Heavy metals linked to cancer, organ damage, and neurological disorders appeared in the samples. Residual solvents can cause allergic reactions. Some inks harboured bacteria that cause severe skin infections.
The letter noted contamination was inevitable: “One container of tattoo ink is used for many customers there by sterility cannot be maintained. The environment in the tattoo shops are not aseptic area.”
Research shows tattoo pigments reach the liver, kidneys, and lymph nodes, raising concerns about long-term exposure.
While further epidemiologic research is crucial to establish a direct causality, the findings underscore the importance of monitoring and controlling the carcinogenic chemicals in tattoo inks to safeguard public health.
One in five people globally now has at least one tattoo. The pigments they carry may remain in their lymph nodes for life, a permanent modification to the immune system whose long-term consequences remain unknown.
(Edited by Muhammed Fazil.)
