What’s in tattoo ink? My team’s chemical analysis found ingredients that aren’t on the label and could cause allergies

Tattoos are an incredibly common form of permanent self-expression that date back thousands of years. Most tattoo artists follow strict health and sanitation regulations, so you might assume that tattoo inks are carefully regulated, too.

But as work done by my team of chemistry researchers suggests, up to 90% of tattoo inks in the U.S. might be mislabeled. This isn’t just a case of a missing pigment or a minor discrepancy. These inks contained potentially concerning additives that weren’t listed on the packaging.

What’s in an ink?

All inks are made up of one or more pigments, which are molecules that give tattoos their color, and some kind of carrier for that pigment. Before the 20th century, pigments used in tattooing included ash, charcoal, minerals or other natural materials. Around the middle of the 20th century, though, tattoo artists started making their own inks using synthetic pigments and dyes.

Today, nearly all pigments used in tattoos are made of synthetic molecules that allow for bright colors – with the exception of white and black pigments.

In the past few decades, tattoo ink manufacturing has shifted from individual artists making their own to large companies manufacturing inks and selling them to artists. My team wanted to figure out whether these inks contained the ingredients advertised, so we analyzed 54 tattoo inks from the U.S. market.

Unlisted ingredients

More than half the inks my research team analyzed contained unlisted polyethylene glycol, also known as PEG. A variety of medical products contain PEG, including laxatives. It can cause allergic reactions, however, and in the case of tattooing, research has suggested that repeated exposure to PEG could lead to kidney failure.

Two carbon atoms, with OH groups at each end.

Polyethylene glycol’s chemical structure.
Jü/Wikimedia Commons

We also found propylene glycol in 15 inks, though it wasn’t listed as an ingredient in any of them. Propylene glycol is generally nontoxic and structurally similar to glycerin, which is used to thicken the ink. Even though propylene glycol is safe for most people, some people are highly allergic to it. In fact, it was the American Contact Dermatitis Society’s 2018 Allergen of the Year.

Three carbon atoms, with OH groups connected to the first and 2nd carbons.

Propylene glycol’s chemical structure.
Edgar181/Wikimedia Commons, CC BY-SA

An allergic reaction to propylene glycol can cause a skin rash, itching and blistering.

In several inks, my research team found unlisted ingredients that are common in cosmetics but have not been tested in tattoo inks. These include BHT, dodecane and 2-phenoxyethanol. In low concentrations, 2-phenoxyethanol can be a preservative. But the Food and Drug Administration has warned that it could get passed to infants through breastfeeding and lead to vomiting and dehydration in babies.

Of the 54 inks we analyzed, 29 reported the correct pigments, while the rest either did not report or reported the wrong pigments. This…

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