THE QUESTION: More than a third of U.S. children live in houses where people regularly smoke. How might parents' smoking affect the youngest of these children?

THE QUESTION: More than a third of U.S. children live in houses where people regularly smoke. How might parents' smoking affect the youngest of these children?

THIS STUDY: Involved 104 infants, 71 with at least one parent who smoked (on average, 16 cigarettes daily) and 33 with nonsmoking parents. When the children were 10 to 12 weeks old, their urine was tested for cotinine, a byproduct of nicotine. In babies with one or more parents who smoked, cotinine levels were more than five times higher than in babies from nonsmoking households. When one parent smoked, levels were higher when the child's mother rather than father was the smoker.

WHO MAY BE AFFECTED? Infants. Although smoke from other people's cigarettes poses risks to all, infants and fetuses face the added risk of potential damage to their still-developing bodies.

CAVEATS: The study did not assess the effect of cotinine on the infants, simply its presence in their bodies. The authors suggested that "by accumulating cotinine, babies become heavy passive smokers."

FIND THIS STUDY: June issue of Archives of Disease in Childhood.

LEARN MORE ABOUT IT: The effects of secondhand smoke at www.cdc.gov/tobacco and www.lungusa.org (click "Quit Smoking," then "All About Smoking").