Certain types of tattoos - including those done with yellow or blue ink, or older and bigger tattoos - are harder to remove than others with laser treatment, according to an Italian study.
Even smaller tattoos done with black ink can take multiple years to erase, and it can be harder to erase tattoos from the skin of people who smoke as well, said researchers whose findings appeared in the Archives of Dermatology.
About half of young people who get a tattoo ultimately choose to have it removed, the researchers said. Laser pulses are used to break up tattoo ink, and the tiny ink particles are then removed by immune cells.
Of 352 people getting a tattoo removed with the so-called Q-switched laser, just under half had their tattoos successfully eliminated after 10 sessions, and three-quarters after 15 sessions, according to the study led by Luigi Naldi, from Centro Studi GISED in Bergamo, Italy.
Smokers, as well as people who had their treatment sessions less than two months apart, were less likely than others to see their body art disappear.
Naldi said that because of the laser's reaction with the individual pigments, yellow and blue inks may change color but not disappear with treatment.
People with those colorful tattoos "should be aware that removal of this tattoo may be more difficult and may not be satisfactory," he told Reuters Health.
The effect of smoking could be explained by smoking's impact on the immune system, he added.
In another study published with Naldi's in the Archives of Dermatology, U.S. researchers tested a new laser device for tattoo removal that involves a shorter pulse - lasting a picosecond, versus the traditional nanosecond.
"With laser treatment for tattoos, no big changes have come about in the past 20 years," said Nazanin Saedi, the lead author of that study from Thomas Jefferson University in Philadelphia.
The Q-switched laser takes so many treatments, she said, and costs add up, discouraging many.
For her study, 12 out of 15 patients completed at least two tattoo removal sessions with the picosecond laser. All 12 had their ink at least 75 percent cleared and were "satisfied" or "extremely satisfied" with the outcome, most after two to four treatments.
Saedi said the company that makes the new device and partially funded her study, Cynosure, is doing clinical trials in hopes of getting the laser approved by the Food and Drug Administration. But for now, it isn't available outside studies.
David Goldberg, a dermatologist who wasn't involved in the studies, said the number of sessions needed to remove a tattoo deters many.
"The number of people getting tattoos continues to increase... which means, when you look at people 10 to 20 years after that, the number of people seeking removal of that tattoo is also higher," said Goldberg, head of laser research in the dermatology department at the Mount Sinai School of Medicine in New York.
There are still limitations to picosecond lasers, including that the machines break down frequently and are very expensive. But he thinks that over the next few years, they will "transform" how tattoo removal is done.
For now, people considering a tattoo should make the decision very seriously.
"It takes about a half hour to get a tattoo, but it can take years to get it removed," he added.