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Tattoo Inks: Poison Pigments?

Credit: iStockphoto/yulkapopkova

Credit: iStockphoto/yulkapopkova

By Ian Musgrave

Allergy and infection are two causes for caution when contemplating a tattoo. But are tattoo pigments toxic, and do they increase the risk of cancer?

Humans have been tattooing themselves for as long as there have been humans, as far as we know. Ötze the Iceman, whose body was entombed in ice for around 5300 years, was tattooed with lines and crosses. Over the millennia, tattoos have wandered between being signs of royalty to being signs of criminality. Since Ötze’s time tattoos have become more complex and colourful, with regional specialisation. In Sir Arthur Conan Doyle’s The Red-headed League, Sherlock Holmes was able to tell that a man had been in China from the shade of pink on the scales of a tattooed fish.

Tattoos are fashionable again, yet in many ways the chemistry of tattoos has advanced little. The commonest pigment for tattoos is still carbon black, although today it is applied with sophisticated needles, instead of cutting the skin and rubbing soot into the cuts, which is how Ötze’s tattoos were made.

Modern tattoos are made by injecting tattoo pigment by needle into the dermis, the layer of connective tissue that anchors the epidermis to the underlying tissue. The chemistry of the tattoo pigment has to ensure that the pigment does not migrate far from the injection site, and that the colour does not fade substantially over time.

For millennia, these conditions were largely met by carbon black and various metal compounds. Today, synthetic colours are part of the tattooist’s armamentarium.

Traditionally, tattoo inks are seen as being biologically inert. However, significant health concerns have been raised over tattoo inks, and a recent ABC radio series (ab.co/1r75FTP) focused on the possibility of carcinogens being present in tattoo inks. What exactly are the risks of toxicity from tattoo inks?

Answering this question is rather difficult, as tattoo inks and tattooing are more complicated than it might seem.

First, we need to consider the types of toxicity – there is acute toxicity (occurring in a relatively short period of time) and chronic toxicity (over weeks to years), and there are also allergic reactions. As well, we need to consider not only the pigments, but the solutions the pigments are suspended in.

Then, we need to consider the tattooing process. The pigment is injected into the dermis, where it is initially distributed in the matrix of the connective tissue, or inside fibroblasts. Over time, macrophages – scavenger cells – take up pigment. Some of the pigment may be transported by the macrophages into the lymphatic system and to the lymph nodes (bit.ly/1ARGANq).

In this way, the material in the tattoo pigments can be exposed to local tissue, and to the body at large. In contrast, the solvents in which the pigments are suspended can rapidly diffuse away, possibly causing more immediate problems.

Allergic reactions to both organic and inorganic pigments are quite common. Tattoo pigments based on metals such as cobalt, cadmium, dichromate and mercury have high risks of allergic reactions. Also, if the pigments are contaminated with nickel sulfate, then they can cause strong allergic reactions. Around 8% of the Australian population is allergic to nickel.

Heavy metal toxicity from metal-based pigments is also possible. Some of the most vibrant colours are associated with toxic heavy metals; the red pigments cinnabar (HgS) and cadmium red (CdSe) are both highly toxic, as is cadmium yellow (CdS, CdZnS) and chrome yellow (PbCrO4).

While there are many reports of local reactions to toxic heavy metals, the degree of chronic exposure is hard to determine. It has been estimated that an 8 cm by 13 cm tattoo contains between 1–25 µg of lead (depending on the degree of lead in the various inks) (1.usa.gov/1tZWxCl). However, how much metal is released from the particles and over what time frame is uncertain.

Heavy metal pigments have largely been replaced by organic pigments (e.g. naphthol-AS for metal-based reds), but as there is limited regulation of tattoo inks in Australia, it is unclear if Australian inks contain substantial amounts of heavy metals. Recent assays of tattoo inks in New Zealand showed that most of them had low levels of heavy metals, although 24% had levels of cadmium over 0.2 mg/kg ink and 22% had levels of lead over 2 mg/kg ink (ab.co/1qe1NLl). Tattoo inks in Australia probably have similar composition and similar heavy metal levels. The incidence of severe adverse reactions to the tattoo pigments is not clear, but one German study reported an overall adverse event rate (including bacterial infections) of 0.02% (bit.ly/1s7kHuH).

The more recent concerns are over the presence of possible carcinogens in tattoo inks. These can be due to the pigments themselves, or to the solvents the pigments are suspended in. It may surprise you that inks based on carbon black – some of the most common inks – are of greatest concern. Ironically, Ötze’s carbon black tattoos may have been for medicinal purposes.

Pure carbon would seem to be a poor candidate for a carcinogen, but it is the chemicals formed during its production that are the main sources of worry. Carbon black is produced by combustion, and in many preparations some polyaromatic hydrocarbons are present. Some, such as benzo[a]pyrene, are known carcinogens; others are suspected of being carcinogens. While benzo[a]pyrene has been detected in some overseas inks (bit.ly/1oYDtxs), it has not been found in Australian inks. Phthalates – also of concern with regards to human health – have been found in some of the ink solvents (bit.ly/1woUN3y).

A significant complication is that, as with the heavy metals, we have no clear idea of the level of exposure to these chemicals. Clearly, a large, detailed tattoo with lots of shading has more potential for carcinogen (or heavy metal) exposure than a small outline tattoo, but if the carcinogenic compounds are largely immobile in the ink particles, then the exposure will be low.

Removal of tattoos (see box p.16) involves a wide range of issues unrelated to the actual toxicity of tattoo pigments themselves and is beyond the scope of this article.

As a reality check, a recent review concluded that any association of skin cancer with tattoos was coincidental. As the highest concentration of potential carcinogens would be in the skin itself, the likelihood that there is a significant general cancer risk is low (bit.ly/1woUN3y).

Tattoos have been part of human life since at least the last ice age, and are increasingly bringing colour into the lives of 21st century Australians. The very chemistry of the tattoo pigments that gives them their vibrant colours produces adverse reactions in some people, more than the average person contemplating a tattoo realises. However, the risk of cancer from tattoos seems very low.

The European Society of Tattoo and Pigment Research was formed in 2013, and its website has some useful general information about tattoos, their risks and questions to ask, covering issues beyond those of chemistry toxicity outlined here. Visit http://tinyurl.com/kktotz2

Ian Musgrave is a molecular pharmacologist/ toxicologist at the University of Adelaide. This article is reproduced from Chemistry in Australia (chemaust.raci.org.au).