Newer pennies pose a special toddler risk.

Toddlers have a habit of mouthing anything within reach, including coins. Last year alone, some 21,000 youngsters ended up in emergency rooms throughout the United States after ingesting these candy-shaped disks--mostly pennies. New evidence indicates that swallowing pennies minted after 1981 poses an especially dangerous threat to children and pets.

Apart from the obvious choking hazard, the pennies can trigger stomach ulcers and erode into circular blades of tissue-ripping zinc, a physician reported this week in Chicago at the annual meeting of the Radiological Society of North America.

Pediatric radiologist Sara M. O'Hara stumbled upon the problem in March 1997, when parents brought a 2 1/2-year-old boy into the Duke University Medical Center in Durham, N.C. Having watched in horror as their child ate a penny and nearly choked, they wanted to know what to do next. Once O'Hara X-rayed the boy and confirmed that the penny was in his stomach, the emergency room staff advised the parents just to wait for the penny to pass in the stool.

But 4 days later, the boy was unwilling to eat, had a persistent stomach ache, and was vomiting blood. When O'Hara X-rayed the boy again, she saw a perforated, "moth-eaten disc" with irregular edges that looked "like something had been nibbling on it." Suspecting it was a piece from some toy, she had another doctor remove it with a tool inserted down the child's throat.

To her shock, what emerged was the penny. She says, "You could just make out the date, 1989, on what was left."

"We had always thought pennies were innocuous visitors [to a child's gastrointestinal tract]," O'Hara explains. However, after 4 days in a child's stomach, this penny had lost one-quarter of its weight, developed dangerously ragged edges, and induced an ulcer in the stomach lining.

Though most pennies will pass through a child safely, O'Hara has since encountered a second eroding penny.

Pennies were once 95 percent copper and relatively inert. In 1982, however, the U.S. Mint began stamping pennies out of zinc coated with a thin veneer of copper. O'Hara suspects that through normal wear and tear, this copper skin can crack, allowing the stomach's hydrochloric acid to dissolve some of the zinc into a toxic, ulcerating soup. She notes that other U.S. coins, made mostly of nickel, pose no similar risk.