For about as long as there have been humans, it seems there have been tattoos.
Ötzi the Iceman, the 5,000-year-old mummy discovered in the Alps in 1991, had 61 tattoos covering his body. And a quick look around the local coffee shop reveals they're just about as popular today. By one estimate, about a quarter of U.S. adults have at least one tattoo.
Yet doctors say we still don't understand the full extent of the skin's reaction to tattoos. There are lots of individual reports of bad reactions to tattoos, some short-lived and others chronic, in the medical literature. And a few European studies lately have tried to put firmer numbers on the extent of those reactions.
"Nobody knows how common these things are," says Dr. Marie Leger, an assistant professor in the Ronald O. Perelman department of dermatology at New York University School of Medicine. "I was really curious."
With the help of two medical students, Leger surveyed more than 300 people they came across in New York City's Central Park.
What did researchers find? Among the tattooed park-goers, 31, or 10 percent, said they'd experienced some sort of adverse reaction after a tattoo. About 4 percent had a problem that didn't last very long, such as pain, infection or swelling. And 6 percent said they'd had a problem that persisted longer than four months, such as itching or scaly skin.
The proportion that reported chronic reactions surprised Leger. "I think that's pretty interesting," she tells Shots. Leger has treated quite a few patients for tattoo reactions. Antibiotics can help with infections and steroids (both creams and injections) can relieve other symptoms.
The findings were published online Wednesday by the journal Contact Dermatitis.
The Central Park survey had some obvious limitations. Foremost among them, the people surveyed described the problems themselves and they weren't independently assessed by doctors as part of the study.
Even when doctors do get involved, it's a challenge to definitively diagnose allergic reactions to tattoo inks, in particular. The reactions can vary quite a bit, and patch testing of inks, a standby in dermatology, isn't very reliable, Leger says.
While there are some well-known tattoo risks, such as infections from needles that aren't sterile, there are lots of open questions.
Tattoo inks, for instance, aren't regulated by the Food and Drug Administration. Agency researchers looking into the inks have learned that a yellow pigment used in inks can be broken down by the body, which might explain why the yellow portions of some tattoos can fade with time.
Still, most people who get tattoos don't have any problems with them, as the Central Park survey found. "It's been my experience that true allergic reactions to the ink are uncommon," says Dr. Elizabeth McBurney, a dermatologist in Lafayette, La., who wasn't involved in the Central Park study.
She's been removing tattoos since the 1970s, and says about 40 percent of her practice now involves helping patients de-ink.
No more than 5 or 10 percent of her patients have medical problems with their tattoos, she says. "The majority of people who come in want the tattoo removed for economic, social or professional reasons," she says. A lawyer or doctor who got a fraternity tattoo in college may want it taken off.
Most often, McBurney uses a laser to remove tattoos. The process requires as many as a half-dozen sessions, which cost hundreds of dollars apiece. "Think before you ink," she says of tattoos. "It's a lot cheaper to put them on than to take them off."