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

(The Conversation is an independent and nonprofit source of news, analysis and commentary from academic experts.)

John Swierk, Binghamton University, State University of New York

(THE CONVERSATION) 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...