09-06 butterfly tattoo

[Image above] Titanium dioxide is the second most common pigment used in tattoo inks—but it could have some adverse effects. Credit: Freestyle Tony, Flickr (CC BY-NC 2.0)

As fall begins to creep into the air on chilly mornings, you may be planning a final camping trip for the year. And as you pack your sunscreen, toothpaste, and assorted snacks into a duffel bag, you may notice a similar ingredient in all these items—additive E171, the regulatory name for titanium dioxide (TiO2).

TiO2 is a white pigment used in almost any product you can imagine, including paints, paper, textiles, cosmetics, food, and pharmaceuticals. The material is produced in two main forms—a regular pigment-grade form, and an ultrafine nanomaterial form. The regular pigment is generally considered nontoxic, but the nano form (which often appears in sunscreen) is still under consideration.

TiO2 is also found in tattoo ink. In fact, it is the second most common ingredient in tattoo ink, where it is usually mixed with bright colors to create different shades.

Self-reports of adverse tattoo reactions often associate delayed healing, skin elevation, and itching with white tattoos and, thereby, TiO2. In 2017, an open-access paper shed new light on the association.

“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,” Bernhard Hesse, coauthor of the study and researcher at the European Synchrotron Radiation Facility, says in a Science Unfiltered article. “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.”

The study raised another question as well—how did the metals iron, chromium, and nickel, which were not part of the ink samples tested, also end up in the lymph nodes?

In a follow-up open-access paper published last month, the researchers made a concerning discovery—those metals came from the tattoo needle and were worn away by TiO2 in the ink.

Compared to black carbon, the most common ingredient in tattoo ink, TiO2 is very abrasive due to its high density and hardness. The effect of this abrasiveness on the metal tattoo needle was evident: “The results show that the pig skin tattooed with TiO2 ink contained by far more Fe-Cr-Ni particles than the skin tissue tattooed with carbon black,” the researchers write in the paper.

And although they note that the sample size is small and the analysis is limited, “ it is beyond doubt that the metal particles derive from the tattoo needle as result of pure mechanical stress.”

Nickel- and chromium-containing wear particles are abraded by TiO2-containing inks. Pigments and wear particles are inserted into the dermal part of the skin, and both are passively and actively transported to the draining lymph nodes. Credit: Schreiver et al., Particle and Fibre Toxicology (CC BY 4.0)

What effect these metal particles have on allergy development and systemic sensitization is still an open question that the researchers say requires more study.

So if you are thinking of getting a tattoo, you may wish to consider inks without TiO2. Instead, consider inks that use graphene—that tattoo could dual as fashion and as a mobile health monitor!

The 2017 open-access paper, published in Scientific Reports, is “Synchrotron-based ν-XRF mapping and μ-FTIR microscopy enable to look into the fate and effects of tattoo pigments in human skin” (DOI: 10.1038/s41598-017-11721-z).

The 2019 open-access paper, published in Particle and Fibre Toxicology, is “Distribution of nickel and chromium containing particles from tattoo needle wear in humans and its possible impact on allergic reactions” (DOI: 10.1186/s12989-019-0317-1).