Although sleazy "scratcher shops" with unskilled artists and dubious safety records are largely a thing of the past, scientists are growing concerned about what's going into tattooed skin, not just how it got there.

New research has turned up troubling findings about toxic chemicals in tattoo inks, including carcinogens and hormone disruptors.

Inks, which are injected into the skin with small needles, have caused allergic rashes, chronic skin reactions, infection and inflammation from sun exposure, said Elizabeth Tanzi, co-director of the Washington Institute of Dermatologic Laser Surgery in Washington, D.C. A study published in July suggested that phthalates and other chemicals may be responsible for some of those problems.

That raises questions about more serious, long-term risks such as skin cancer, scientists say.

One of the chemicals found in black tattoo inks, benzo(a)pyrene, is a potent carcinogen that causes skin cancer in animal tests. Dermatologists have published reports in medical journals on rare, perhaps coincidental cases where malignant melanomas are found in tattoos.

Recently, the Food and Drug Administration launched new studies to investigate the long-term safety of the inks, including what happens when they break down in the body or interact with light. Research already has shown that tattoo inks migrate into people's lymph nodes.

For now, it's unclear what, if any, long-term health risks are posed by tattoo inks.

More people inked

An estimated 45 million people in the United States, including 36 percent of adults in their late 20s, have at least one tattoo, according to estimates by the FDA and a Harris Interactive Poll.

Most customers are concerned with how the tattoo will look years down the road.

"People usually don't come in worried about health concerns," said Mario Delgado, owner of Moth and Dagger Tattoo Studio in San Francisco. "People are more concerned about getting a good tattoo."

In July, German scientists reported that the chemical dibutyl phthalate, a common plasticizer, is found in black tattoo inks. In the study of 14 commercially available inks, they found low levels of the chemical in all of them and determined the substance could be the reason for adverse skin reactions.

With phthalates, which can mimic estrogen or disrupt testosterone, potential effects on fetuses and infants are the major concern. In infant boys, prenatal exposure to dibutyl phthalate has been linked to feminization of the reproductive tract.

But phthalates in tattoo inks may not carry the same risk.

"While this is a potential source of high exposure, it might not last very long and may not present a risk to health," said Joseph Braun, an environmental epidemiologist at Harvard University.

Metals found as well

Heavy metals such as lead, which can harm the reproductive and nervous systems, also were found in a study of 17 different black inks from five manufacturers.

Colored inks often contain lead, cadmium, chromium, nickel, titanium and other heavy metals that could trigger allergies or diseases, scientists say. Some pigments are industrial-grade colors that are "suitable for printers' ink or automobile paint," according to an FDA fact sheet.

Black tattoo inks, which are usually made of soot, contain products of combustion called polycyclic aromatic hydrocarbons, according to a 2010 study by the German scientists.

The PAHs in the inks include benzo(a)pyrene, which was identified in an Environmental Protection Agency toxicity report as "among the most potent and well-documented skin carcinogens." It is so potent that it is routinely used in animal tests to grow tumors. It also has been linked to skin cancer in shale oil workers.

"Tattooing with black inks entails an injection of substantial amounts of phenol and PAHs into skin," wrote the German scientists. They said the PAHs could "stay lifelong in skin" and "may affect skin integrity," which could lead to skin aging and cancer.

Scientists are debating the possible tattoo-cancer link, based so far on a handful of malignant melanomas found in tattoos and reported in medical literature.

"Even though cases of malignancies such as melanoma, basal cell carcinomas, squamous cell carcinomas and keratoacanthomas have been reported for the past 40 years, it remains unclear what role tattoos play in their pathogenesis," wrote scientists from France's University of Montpellier in a 2008 study.

FDA's role

The FDA has the power to regulate tattoo inks and any added colorings. But the agency has never flexed its regulatory power, citing lack of evidence of safety concerns and other priorities.

In 2003 and 2004, the FDA received its largest cluster of complaints, more than 150, from people on the giving and receiving end of tattoos. Since then, the FDA has begun more research on tattoo inks.

One major question investigated by the FDA is where does the ink go when the tattoo fades?

Preliminary results show that a common pigment in yellow tattoo inks, Pigment Yellow 74, may be broken down by the body's enzymes, according to the FDA. Sunlight also breaks it down into colorless components of unknown toxicity. Also, when skin cells containing ink are killed by sunlight or laser light, the ink breakdown products could spread throughout the body.

Previous studies have shown tattoo inks move into the lymph nodes, but whether that is a health risk is not known, according to a 2009 FDA consumer update. Lymph nodes are part of the body's system for filtering out disease-causing organisms.

Because of the chemicals involved, California's Proposition 65 requires all tattoo shops to warn customers of exposure to carcinogens. The warning is included in the release forms that people must sign before getting tattooed in California.