One recent study of 7,960 college students in Texas found that one in five had at least one tattoo or piercing of a body part other than the earlobe.

But health officials say they are increasingly worried about the health risks posed by such body modification practices, including physical disfigurement and bacterial and viral infections, and not only from needles that draw blood in potentially unsanitary conditions.

The primary concern is infection with blood-borne pathogens like H.I.V. and the C and B forms of the hepatitis virus. But doctors say that tongue and genital piercings can also provide channels for bacteria and viruses to enter the bloodstream after the piercing procedure. Bacteria that live on the skin, including some penicillin-resistant forms of staphylococcus, are easily spread by unsterilized instruments or ungloved hands. And bacterial infections – or the body’s reaction to the insertion of a foreign object – can cause deformities at piercing sites.

Last month, Senator Charles E. Schumer, Democrat of New York, joined with health officials from Long Island to express concern over a growing number of hepatitis C cases, linking the increase in part to body piercings and tattoos. The potentially fatal virus can live in the body for decades without symptoms.

Studies have not conclusively demonstrated a connection between body modification and hepatitis C. The Texas study, sponsored by the Centers for Disease Control and Prevention, found that college students with piercings, tattoos or both were no more likely than other students to have been exposed to the hepatitis C virus. But an earlier study reported that of 626 patients at an orthopedic clinic, those with tattoos were seven to eight times as likely to have subclinical hepatitis C infections.

“Regardless of whether or not we can demonstrate that bacteria or viruses are spread in this manner, anything that pierces the skin and has blood on it can potentially spread an infection,” said Dr. Miriam Alter, associate director for science at the C.D.C.’s division of viral hepatitis and the agency’s lead scientist on the Texas study. “The moment you pierce the skin barrier, there is risk for transmission of a disease.”

Licensing requirements for tattoo and piercing establishments, the growth of professional organizations for practitioners and the growing sophistication of Internet-educated consumers have increased safety. Most people who seek tattoos know that they should see the artist remove a new needle and tube setup from sealed plastic and that fresh ink from disposable containers should be used.

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