(NewsNation) — Researchers studying the composition of tattoo inks have discovered that those used in the United States may contain cancer-causing chemicals.

In the study presented this week at an American Chemical Society conference, Dr. John Swierk said little is known about the chemical composition of inks, which are mostly unregulated in the U.S.

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During their analysis of inks, Swierk and his team discovered the presence of ingredients that were not listed on the label. In one case, ethanol was not listed, but the chemical analysis showed it was present in the ink.

“Every time we looked at one of the inks, we found something that gave me pause,” Swierk said in a news release from the American Chemical Society. “For example, 23 of 56 different inks analyzed to date suggest an azo-containing dye is present.”

It’s those azo pigments that raise concerns.

While they cause no health problems when chemically intact, bacteria or ultraviolet light can degrade azo pigments into a compound that is a potential carcinogen, according to the Joint Research Centre.

The European Union has recently cracked down on tattoo inks, placing a ban on certain blue and green pigments. Americans should assume that those pigments of concern are in their tattoo inks, Swierk said at the conference.

“I think it’s important to note that those particular pigments, Blue 15:3 and Green 7, have been used in tattooing for a very long time,” he said. “While the EU’s data is a concern, it’s not a definite. Much like with everything involving tattooing, it’s incumbent on consumers and artists to make a decision about their particular comfort level and then proceed accordingly.”

In addition to ink ingredients, Swierk and his team noted a red flag in particle sizes, with some measuring as small as 100 nanometers.

“When you get down to that size regime, you start to have concerns about nanoparticles penetrating into cells, getting into the nucleus of those cells, doing damage and causing cancer that way,” Swierk said.

After the team has conducted more tests and their research is peer-reviewed, it will be posted on their website.

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“With these data, we want consumers and artists to make informed decisions and understand how accurate the provided information is,” Swierk said.