People seeking to get a tattoo should be picky about the parlor they have them done at, US researchers say in the wake of a study that found a link between body art and Hepatitis C, the leading cause of liver cancer.

According to the study, which appeared in the journal Hepatology, people with the blood borne hepatitis C virus, were almost four times more likely to report having a tattoo, even when other major risk factors were taken into account

“Tattooing in and of itself may pose a risk for this disease that can lay dormant for many, many years,” said study co-author Fritz Francois of New York University Langone Medical Center, although he warned that the study could not produce a direct cause and effect.

About 3.2 million people in the United States have hepatitis C, and many don't know because they don't feel ill, according to the U.S. Centers for Disease Control and Prevention (CDC).

Hepatitis C is the leading cause of liver cancer and the most common reason for liver transplants in the U.S. Some 70 per cent of people infected will develop chronic liver disease, and up to 5 per cent will die from cirrhosis or liver cancer.

For the current study, researchers asked almost 2,000 people about their tattoos and hepatitis status, among other question, at outpatient clinics at three New York area hospitals between 2004 and 2006.

They found that 34 per cent of people with hepatitis C had a tattoo, compared to 12 per cent of people without the infection.

The most common routes of infection for hepatitis C are through a blood transfusion before 1992 or a history of injected drug use. Injected drug use accounts for 60 per cent of new hepatitis cases a year, but 20 per cent have no history of either injected drug use or other exposure, according to the CDC.

Francois and his colleagues only included people with hepatitis C who did not contract it from these two other common sources.

After accounting for other risk factors, the difference between people with and without hepatitis was even greater, with four times as many tattoos in the infected group than for uninfected people.

“This is not a big surprise to me,” said John Levey, clinical chief of gastroenterology at the University of Massachusetts Medical School in Worcester. Earlier studies had found a link, but they were small and had not taken other risk factors into account as well as the new study did.

But the CDC's Scott Holmberg said the link may not be quite as strong as the findings suggest, because some people who used illegal drugs probably would not admit it, even on an anonymous questionnaire. And they didn't rule out people who picked up hepatitis before getting their tattoo.

Holmberg recommends that people only have tattoos or piercings done by trained professionals, noting that there have been no reports of hepatitis C outbreaks linked to professional tattoo parlors in the United States.

Tattoo parlors are not federally regulated, and standards vary by state and region. The Alliance for Professional Tattooists recommend finding a tattoo artist who wears disposable gloves, a clean work space without blood spatters and single-use disposable needle kits.