Three in 10 people in America have a tattoo, and those in the 18 - 34 age bracket, it's almost 40 percent. But what's in those inks, exactly? NPR science correspondent Nell Greenfieldboyce talks about what researchers currently know about tattoo inks. It's not a lot, and researchers are trying to find out more. Email the show at [email protected]).Learn more about sponsor message choices: podcastchoices.com/adchoices)NPR Privacy Policy)