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 a 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.
But Dr. David Graham, director of public health for the Suffolk County, said that it was impossible to police everyone.
"There will always be someone driven by profit who will avoid regulatory guidelines and licensing fees," he said. And even establishments that use fresh needles and surgical gloves, spray disinfectants and heat-sterilizing autoclaves are of concern, scientists say.
It is estimated that 1 piercing in 10 becomes infected. Staphylococcus bacteria, which can live on the skin and in the nose, is a frequent cause, said Dr. Scott Hammer, professor of medicine at Columbia College of Physicians and Surgeons.
"If you disinfect the surface of the skin, but use a forceps that has not been sterilized, you are risking spreading infection," Dr. Hammer said.
"You don't need a puncture; you only need an abrasion for the organism to cause an infection."
People who have piercings should also be aware that a penicillin-resistant strain of the bacterium Staphylococcus aureus has cropped up in the last two years, Dr. Hammer said. Once rarely seen outside medical settings, the strain recently has been traced to group settings like sports and fitness clubs and military barracks.
In Oregon, new laws regulating piercings were drafted in response to an outbreak of an antibiotic-resistant strain of the bacterium Pseudomonas aeruginosa in ear cartilage. Health officials traced it to a piercing gun at a jewelry kiosk. Four people were hospitalized; permanent ear deformities, including the removal of ear cartilage, resulted.
Experts warn that such infections are more common -- and more difficult to treat -- in ear cartilage because of its limited blood supply. They also advise against the use of piercing guns that crush flesh rather than lacerate it and that cannot be properly sterilized.
Unlike most tattoos, which scab over and heal in one to two weeks, piercings can pose problems in the long haul. Nipple piercings that go too deep have damaged tissue and led to problems in breastfeeding after the jewelry was removed.
Stud earrings can become embedded in nipples, navels or elsewhere when the body tries to "heal over" the piercing site. Clothing can catch on navel jewelry, causing irritation, infections, and tears.
Keloids, the overgrowth of scar tissue, can also cause disfigurement, including tumorlike growths.
Some styles of mouth and genital piercing carry other dangers. Dr. Jay Gohel, a dentist at the Smile Institute in Manhattan, said tongue rings could cause trauma and breakage of the upper teeth, including the lingual cuspids and molars.
"Every time you move the tongue it's banging on the teeth," Dr. Gohel said. "It's like tapping on the glass over and over again. It finally breaks."
He said he had restored several teeth broken in this way.
Dr. Gohel and other experts have also seen infections from tongue piercings. One study reported on the case of a 25-year-old man with a potentially fatal disease of the heart's inner lining that was traced to his tongue piercing. Many people use antibiotics as a preventive measure before dental surgery because of congenital heart disease, heart defects or repair heart valves. Dr. Nieca Goldberg, chief of women's cardiac care at Lenox Hill Hospital in New York, said that people in high-risk categories might not realize that they should also take protective medication before piercings.
"You may think of a piercing as cosmetic, but if you have mitral valve prolapse, a heart murmur or other conditions that require antibiotics before dentistry, you should be treating a piercing the same way," Dr. Goldberg said.
Many middle-aged doctors seem unaware that tongue and genital piercing are often done for additional stimulation in sex, oral sex in particular. Genital piercings not only run the risk of wearing condoms, but they may also tear or abrade the flesh during sexual intercourse, allowing disease transmission through blood or other body fluids.
While most piercings will close up or leave minimal scarring over time once jewelry is taken out, tattoo removal is often costly and painful. At the Skin Institute of New York, removing a tattoo takes 6 to 10 sessions, at a cost of $300 to $800 each, said Dr. Lance H. Brown, clinical assistant professor of dermatology at the New York University School of Medicine.
He uses a Q-switch laser to break down the pigment in the tattoo ink. The switch allows him to adjust the laser wavelength to match the wavelength of the pigment he is attacking. "The laser explodes particles of ink, then the body's macrophages come and essentially eat up the debris," Dr. Brown said. The sessions stretch over weeks because the body can only absorb so much waste at one time.