Infographic on tattoo chemistry, colourants and concerns. Tattoo ink contains carriers and colourants. Historically, ground up minerals were used as tattoo pigments, but today most colourants are organic compounds, primarily azo dyes. Some of these pigments break down into compounds with known health concerns, though a causative link between tattoos and cancer has not been established.
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A lot of people have tattoos: an estimated 12% of Europeans and 24% of Americans. What’s in tattoo ink, and how are different coloured tattoos produced? This graphic for National Tattoo Day (July 17) takes a look.

While surveys give us an idea of how many people have tattoos, we know less about the specifics of tattoo ink. They’re largely unregulated, so the contents of a particular tattoo ink might not always be clear. However, we do know plenty about their general composition and the roles their constituents play.

The two key components of tattoo inks are carriers and colourants. Carriers are solvents which help transport the colourants below the top layer of the skin. These are commonly ethanol or distilled water. Other compounds such as isopropyl alcohol are also used in some formulations.

Colourants are what give tattoos their colour. Over 100 different pigments have been found in studies of various tattoo inks. The tattooing process deposits pigments in the dermis layer of the skin.

Historically, metal-containing pigments were used for tattoo inks. These included cinnabar (mercury(II) sulfide) for bright reds and chromium oxide for greens. If you’re familiar with these elements, you’ll know that they’re known for their toxicity! For this reason, a number of these metallic pigments are no longer used in the present day.

Instead, tattoo inks use organic (carbon-based) pigments. These come from a various families of compounds, including azo dyes for reds, yellows and oranges, and phthalocyanine dyes for blues and greens. It’s estimated that over 80% of tattoo ink colourants are now organic compounds. 60% of these are from the azo dye family.

When you first get a tattoo there’s a possibility of infection or allergic reaction. But there’s growing concern that compounds in the tattoo ink could sometimes pose a health risk, too.

Some compounds of concern are those found as impurities in the tattoo inks, such as polycyclic aromatic hydrocarbons (PAHs). PAHs are largely found in black inks and are impurities from pigment production. They include compounds such as benzo-[a]-pyrene, a known carcinogen.

Other problem compounds are additions to the formulation which act as preservatives or perform some other role. These include formaldehyde (a preservative) and benzoisothiazolinone (an antiseptic). The former of these is a carcinogen, whereas the latter causes skin irritation in some people.

The colourants themselves could also lead to longer term problems. Some azo dyes break down due to bacterial action or in the presence of UV light from the sun, forming primary aromatic amines. These compounds are classified as carcinogenic.

As mentioned previously, tattoo inks are largely unregulated at present. However, with the growing concerns, countries are starting to look at introducing rules around the chemicals used in the inks. The European Commission is working on legislation to restrict over 4,000 substances in tattoo inks, including phthalocyanine dyes.

In the meantime, should you worry if you have a tattoo? The good news is that a causative link between tattoos and cancer hasn’t been established. A review of current evidence in 2012 found that “the number of skin cancers arising in tattoos is seemingly low, and this association has to be considered thus far as coincidental.” While a link can’t be ruled out, and long term effects are still unknown, future planned regulations should make tattoo inks safer.

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