Researchers just exposed what's in tattoo ink — and it’s a ‘significant problem’

Okay, fair enough.

"If you wanted one now, would you reconsider getting it, especially after your research?" I prod.

"Sure, but I think I would stick to black inks and try to be a little selective there," Swierk says.

Tattoos have been around for millennia, used for ceremonial, religious, symbolic, and artistic reasons. But the inks used for tattoos are largely unregulated in the U.S., which has resulted in products whose components are a mystery. Swierk and undergraduates in his laboratory were interested in determining exactly what components went into tattoo inks. So, they began analyzing inks and have so far looked at more than 50 different inks and reported that even when the products included an ingredient list on the label, the lists weren't accurate.

What's worse is the team also detected small particles in many inks that could be harmful to human cells.

Getting to the bottom of the ink barrel

Swierk and the team realized that very little information about the composition of tattoo inks was public knowledge, so they began analyzing popular brands.

To begin with, they interviewed tattoo artists to see what they knew about the inks used on customers. They were somewhat surprised to find that the artists could identify a brand they preferred, but they didn't know much about its contents. No dye manufacturer appeared to make pigments specifically for tattoo ink. "Big companies manufacture pigments for everything, such as paint and textiles. These same pigments are used in tattoo inks," Swierk says. Although tattoo artists must be licensed in the locales where they operate, for safety reasons, no federal or local agency regulates the contents of the inks themselves.

Tattoo inks contain two parts: a pigment and a carrier solution. The pigment could be a natural pigment, such as bone char or wood ash (soot), which was used in traditional tattoos; an organic azo or polycyclic compound, like the two commonly-used green and blue pigments recently banned for use in tattoos in Europe; a solid mineral compound such as titanium dioxide, which is white; or a combination of different types of compounds, such as those often used to produce blue ink. The carrier solution transports the pigment to the middle layer of skin and helps make the pigment more soluble. It can also be used to control the viscosity of the ink solution and sometimes includes an anti-inflammatory agent. Inks may also contain surfactants, binding agents, fillers, and preservatives.

Swierk’s team has been investigating the particle size and molecular composition of tattoo pigments using Raman spectroscopy, nuclear magnetic resonance spectroscopy, and electron microscopy. From these analyses, they have confirmed the presence of ingredients that aren’t listed on some labels. For example, 23 out of 56 different inks analyzed to date suggest the presence of an azo-containing dye. Although many azo pigments do not cause health concerns when they are chemically intact, the Joint Research Centre, which provides independent scientific advice to the European Union, states that bacteria or ultraviolet light can degrade these into another nitrogen-based compound that is a potential carcinogen.

Interesting Engineering sat down with Swierk to give us an insight into the groups' tests, and the many questions we probably need to be asking before getting a tattoo.

This interview has been edited for length and clarity.

Interesting Engineering: Based on your research, do you think people genuinely care what's in their ink?

John Swierk: I think there are different reasons that people care. Some care in terms of potential safety, and some in terms of usability. An artist cares about factors such as how well it goes into the skin and stays in it. And how well the color holds. I think nobody is hostile to the idea of making sure the tattoo inks are safer. It's just that people have different definitions of what that might be.

IE: Why do you think tattooing is largely unregulated in the US? I believe it's different in the EU.

JS: It is. So the European Union has much more stringent regulations about tattooing. In the U.S., I think it's a combination of factors. One, the Food and Drug Administration (FDA) has a lot of things that they need to regulate. And tattoo inks are generally elective. So I think a lot of the effort is put into things that people have to have and don't have much choice [like food]. Whereas, you have the choice usually to get a tattoo, and so you're making a conscious decision there. That's a big part of it - people who are getting a tattoo are choosing to get one. And I think from the FDA's perspective, if you're going to make that choice, then you're an adult and you can live with that choice.

IE: Were there any previous discoveries that led to your current study?

JS: Sure, maybe 15 years ago, there was a bit of work in Europe, some concerns with heavy metals and with the improper labeling of ink bottles. But initially, our focus was more on how light causes a tattoo to break down. But then we realized that nobody's really looked at tattoo inks in the U.S. market to see what's in there. And so there was a real gap in terms of understanding and we knew that we have the tools and the expertise to potentially address that gap. And that could be an interesting place for us to start.

IE: How much of a breakthrough is the research?

JS: So, we are looking at commercial tattooing through a variety of techniques to try to understand the different components in these inks, and then looking to see how closely or accurately information on the labels or the Material Safety Data Sheets are. We look at everything - from trying to identify the specific pigments that are in the inks to what's in the carrier packages, and what solvents are present. I don't think we found an ink where we felt like the reported information was complete and accurate. It could be minimal things like the label would say it contains grain alcohol, but it actually also contains rubbing alcohol, or it could be something more serious like listing incorrect pigments. We're not at a point where we've finished looking at every ink in the market. So I don't want to say that that's a problem that's common to every commercial tattooing, but certainly, it's a significant problem within that market. And we're just beginning to understand the scope of the problem, too.

IE: The team analyzed 16 inks using electron microscopy, and about half contained particles smaller than 100 nm, which is a concerning size range that can get through the cell membrane. How harmful is it?

JS: The best answer is I honestly don't know. I mean, I think there are a lot of people out there studying the impact of nanomaterials on human health. And what they seem to be saying is that we should avoid particles that are less than 100 nanometers. That would seem to imply that there are some safety concerns there that we should be mindful of. There is plenty of evidence in the literature about pigments migrating within the body just on their own. There are a lot of stories about pigments collecting in lymph nodes, so we know that they're becoming mobile, and we know that they're working their way through the body. So I think with the recognition of those two things, certainly, you would look at that and say, gosh, maybe we should be making sure the particles are a little bit larger.

There are a lot of stories about pigments collecting in lymph nodes, so we know that they're becoming mobile, and we know that they're working their way through the body.

IE: Has the study been peer-reviewed yet?

JS: No, we're still working our way through as many of the things as we can before we send it for peer review. So that's why I'm a little hesitant to talk in absolutes. Because we haven't looked at every manufacturer. We're confident in our data, but I don't want to specifically call out an ink manufacturer or talk specifics until the study has gone through peer review, and other people have looked at what we've done and agreed with our interpretations or disagreed, perhaps.

IE: Right. Does that also mean you expect controversy?

JS: I think there will be some intersection with the tattoo community. Generally, I think of tattoo artists as being pretty serious professionals, people that want to do a lot and be the best they can at their craft. And so you meet a lot of tattoo artists that are very enthusiastic and happy that you're doing this kind of work, that you're looking into it and trying to push for safer, better tattoos. But at the same time, you also meet some folks that are concerned about - is the research going to lead to regulations? Is it going to impact their business? Is it going to impact the types of colors that are available? And they very reasonably point out that while the EU has raised some concerns about the pigments, particularly blue and green pigments, a lot of people have gotten tattoos over a lot of years, and there's no obvious threat to human health that we're aware of.

But does that mean that there's a concern that we haven't identified because we don't know what to look for? Does that mean that as the market for tattooing grows, problems might not develop? No, but they would argue that tattooing seems to be an inherently safe process, and therefore, we shouldn't be looking. To me, that's a little bit of a narrow focus. Perhaps it's a little premature to assume that it's inherently safe. We're just interested in helping artists and customers have the best safest products that they can.

IE: In that case, did you face any kind of obstacles during the research?

JS: Yes. The project has proven to be much more complex than we ever imagined. And in large measure, it's because, while there's been a lot of great work over the years on tattoos, we still objectively don't have a great understanding of them - of what's in the commercial links, what their impacts are on cells and how light factors into this. It almost feels at times like there's more that we don't know than we do know. Normally, in science, you're building off of a lot of established research and you've got a foundation to go up. At times it sort of feels like we're really breaking new ground on this. And so, it's been an interesting challenge in that respect to sort of figure out, how do we do this, how do we separate it, how do we get an accurate read on these pigments, things like that. It's been a lot of fun, but it's definitely been complex.

IE: Was that surprising? Considering tattoos were around for centuries.

JS: Well, I don't want to say there was nothing we couldn't build on. But, you know, it's not an area of science that's really highly developed, compared to others. So there wasn't a really good understanding of tattoos not being exposed to light for us to work off of. I think it did surprise me. And I think it surprises a lot of people because tattoos are so common and so ubiquitous, you sort of assume that we understand them because there are a lot of state and local regulations for tattoo shops. You sort of think that at the highest levels, there would be more oversight on inks and a better understanding of the science. And it turns out that there isn't.

IE: What are the questions that you think we should be asking when it comes to tattooing?

Well, that's a great question. Let me think about it.

The biggest question and the one that motivates us is what happens when you expose a tattoo to light. What is it breaking down into? You may have inks and pigments that are perfectly safe, but usually, when they're exposed to light and decompose photochemically, it results in the formation of things that are not so safe. And so, we don't know if that happens, but we also don't know that it doesn't. I think it's the same questions that the EU is asking. What are the pigments we should have concerns over? And why? And do those concerns translate into humans or at least animal models? You know, the reason I think a lot of research sort of dried up a decade ago, in the U.S., is because they stopped allowing the use of animal models. And I know that's ethically complicated, it's our best way of studying these things and understanding what happens.

Another great question is what is a tattoo on human skin look like? We do have a picture that we think is reasonably good. That was published a few years ago, but it still hasn't been, to my knowledge, sort of validated in a human system or an animal model system. To be honest with you, I don't even know what some of the questions should be, because we don't know what we don't know. So honestly, the best answer to your question is you can ask almost any question about tattoos because we probably don't have a rigorously detailed answer.

IE: So your next step would include working with more inks, correct?

Yeah, we actually have multiple project lines going on. One direction is just looking at commercial links. And we've looked at six or seven manufacturers and a lot of the bigger names, but there are still a few we haven't looked up. And we'd really like to continue to get as many analytical details as we can on these inks.

And then we're also doing some studies on model human dermal cells to look at possible trends and toxicity. Certainly, people have looked at this before, but one of the challenges is that you have a study that might look at one or two pigments, and another study that looks at a couple of different pigments, and they're not using necessarily the same assays or collected under the same conditions. And so, we're trying to look at one, just general toxicity, or potential toxicity in these pigments, and then also start thinking about what happens when they're exposed to light. We're doing some work on actually watching the breakdown of embedded tattoos under laser illumination to study that process. So we have a lot of next steps, but I think on this specific project, the next steps are to try to reach a point where we think, okay, we've done a pretty good job of serving the U.S. market, and now we need to publish and get the results out.

Swierk and the team will add the information to their website "What’s in My Ink?". The data could help consumers and artists make informed decisions, understand the accuracy of the provided information, and answer their many, many questions.

The researchers presented their results at the fall meeting of the American Chemical Society.

Study abstract:

The composition of tattoo inks is widely unknown due to the lack of FDA regulation. Work is being done to separate the different components in the ink and identify them through different analytical techniques including UV-visible, IR, NMR, and Raman spectroscopies, LCMS, microwave acid digestion, and ICP-MS. Tattoo removal is also a cause for concern as it is not known how the ink breaks down or what products form. Similar analytical techniques can be used to analyze these photoproducts after laser photolysis focusing on products potentially harmful to human health.