Scientists were already aware that pigments from tattoo ink can travel to the lymph nodes, critical components of the immune system that help fight off viruses and bacteria. Cutting edge X-ray technologies have now provided a look at what much smaller, and more toxic particles within the ink get up to, suggesting that these too can make the migration.

"We already knew that pigments from tattoos would travel to the lymph nodes because of visual evidence: the lymph nodes become tinted with the color of the tattoo," says Bernhard Hesse, one of the two first authors of the new study. "It is the response of the body to clean the site of entrance of the tattoo. What we didn't know is that they do it in a nano form, which implies that they may not have the same behavior as the particles at a micro level. And that is the problem: we don't know how nanoparticles react."

Tattoo ink contains a wide range of organic and inorganic pigments, along with preservatives and contaminants such as nickel, chromium, manganese and cobalt. Two of the most common ingredients are the materials carbon black, for dark tattoos, and titanium dioxide (TiO2), a white pigment often mixed with other colors for shading.

While TiO2 is used in food additives, sun screens and paints, its use in tattoo ink is thought to bring side effects such as skin elevation, itching and delayed healing. Scientists at the European Synchrotron Radiation Facility have gained a new insight into its behavior in tattoo recipients, using their stadium-sized synchrotron machine to track TiO2 particles in the skin.

A synchrotron works by shooting different beams of X-ray light through lenses and instruments onto a sample to observe the behavior of matter at a molecular and atomic level. Applying this technique to ex-vivo tattooed tissue samples, the team was able to track both micro and nanoscale TiO2 particles, and found that the latter were indeed transported to the lymph nodes. The team reports strong evidence of the "long-term deposition" of toxic elements in the body, which they say could lead to chronic enlargement of the lymph nodes.

"When someone wants to get a tattoo, they are often very careful in choosing a parlor where they use sterile needles that haven't been used previously," explains Hiram Castillo, one of the authors of the study and scientist at the ESRF. "No one checks the chemical composition of the colors, but our study shows that maybe they should."

From here, the team plans to conduct further research exploring the links between the chemical structures of tattoo pigments and adverse effects using patient samples.

The research was published in the journal Scientific Reports.

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