Tattooing has been a human practice for thousands of years. The mummy of Ötzi – the remains of a man found in 1991 in the Ötz Valley, in Austria, 5,300 years after having been murdered by blows and arrows – had 61 skin punctures filled with charcoal ashes, according to the investigation carried out by Albert Zink, director of the Institute for Mummies and the Iceman, and published in the Journal of Cultural Heritage. The ornamental, sentimental, ritual, personal or superstitious decoration of the skin is booming (between 9% and 30% of the population is tattooed, depending on the country); but, although health authorities monitor the composition of today’s inks, some of their components elude conventional analysis. A team of researchers at Binghamton University (State University of New York), recently analyzed a hundred common tattoo inks and found ingredients that are not listed on the labels, as well as some potentially harmful particles.
The investigation – the results of which were presented Wednesday at the fall meeting of the American Chemical Society – started off in a different direction. According to lead researcher John Swierk, the team intended to study the effects of lasers for tattoo removal. But then he realized how little is actually known about the composition of tattoo inks, so they started to analyze the most popular brands.
Tattoo inks contain a pigment and a carrier solution. The former may be a molecular compound, such as a blue pigment; a solid compound, such as titanium dioxide, which is white; or a combination of the two, such as light blue ink. The carrier solution takes the pigment to the middle layer of the skin and usually helps make the pigment more soluble. It can also control the viscosity of the ink solution and sometimes includes an anti-inflammatory ingredient.
But that is only the general description. Technology has been key to revealing the molecular composition of the smallest pigment particles. Techniques such as Raman spectroscopy (which uses the interaction of the light with the chemical bonds of a substance to determine its structure), nuclear magnetic resonance and electron microscopy have made it possible to detect ingredients that were not listed on labels, like ethanol. “Every time we looked at one of the inks, we found something that gave me pause,” explains Swierk, who clarifies that none of the tattoo artists who have collaborated in the investigation knew the composition of the products that they use.
The analyses found azo pigments in 23 brands of ink. Azo pigments are used for coloring textile and leather articles. According to the researcher, no tattoo product establishment makes specific products; it is the large companies the ones who manufacture pigments for everything, such as paints and textiles, and those are the ones that are used in tattoo inks.
Azo pigments do not pose a health problem as long as they remain chemically intact, but the Joint Research Center, which provides scientific advice to the European Commission, warns that bacteria or ultraviolet light can degrade them into another nitrogen-based compound that is a potential carcinogen.
According to the European report Safety of Tattoos and Permanent Makeup, azo pigments, in some cases, can release aromatic amines, which are linked to some types of cancer, such as bladder cancer, and are intended for use in the rubber, aluminum and textile industries. In the latest regulation, the concentration of these pigments is limited.
Through electron microscopy, the team also identified particles smaller than 100 nanometers (nm) in eight inks. A nanometer is one millionth of a millimeter; according to Swierk, the range found is concerning because “particles of this size can get through the cell membrane and potentially cause harm.”
The Binghamton researchers do not consider the investigation closed and will continue to uncover the composition of the tattoo inks. The results will become part of the What’s in My Ink? website, so that consumers and artists can make informed decisions and understand how accurate the information they receive is. This website explains that some pigments may include low levels of cadmium, mercury and lead, or concentrations of chromium greater than one particle per million, the maximum recommended to avoid allergic reactions.
The Food and Drug Administration warns of the possible adverse effects of a tattoo: infections, scars, allergic reactions, granulomas (nodules around the pigment, which the body perceives as foreign) and some minor complications during MRIs.
However, there is also a positive side to tattoos, related to their therapeutic uses. Cristina Zabaleta, from the University of Southern California, uses ink to improve cancer diagnosis. The author of a study published in Biomaterials Science, employs dyes incorporated into nanoparticles that provide a more effective image contrast in the identification of tumor cells.
The tattoo technique has other applications. A team from the University of Missouri has studied how to create on-skin bioelectronic devices using pencils with 93% graphite content. Assistant professor of engineering Zheng Yan explains that, while the conventional approach to developing a biomedical electronic device on the skin is often complex and can be expensive to produce, this approach is low cost and quite simple.
Francesco Greco, from the Graz University of Technology, has developed “tattoo electrodes,” conductive polymers made from standard tattoo ink that stick to the skin. Tattoo electrodes can record electroencephalographic (EEG) signals of the highest quality because “brain waves are in the low frequency range and EEG signals have a very low amplitude. They are much more difficult to capture in high quality,” says Laura Ferrari, who worked on this project.