In the experiment, described March 6 in the
Journal of Experimental Medicine, macrophages gobbled up the ink as expected, but did not digest and remove it. Instead, the cells held onto the ink until the researchers killed the cells. About 90 days later,
new macrophages moved in and reabsorbed the ink. This capture-release-recapture cycle was key to preserving the tattoos, the researchers say.
But a mouse study doesn’t settle the science of tattoos in humans, says Desmond Tobin, a dermatology expert at the University of Bradford in the United Kingdom, who was not involved in the study. Macrophages may live longer in humans than in mice, and the persistence of those cells might be responsible for preserving tattoos in human skin, he says.