Children who are exposed to secondhand tobacco smoke early in life are at greater risk of being hospitalized for infections than those brought up in a smoke-free environment, researchers from Hong Kong report.

The risk of being hospitalized was greatest among babies six months old and younger, but the increased risk persisted up until the children were 8 years old, Dr M. K. Kwok of the University of Hong Kong and colleagues found.

Children who were premature or low birth weight were particularly vulnerable. The findings suggest that secondhand smoke exposure may not only be harmful to children's respiratory tracts, but to their immune systems as well, Kwok and colleagues say. Hong Kong banned smoking in public places in 2007, but babies and children may still be exposed to secondhand smoke at home, the researchers note in their report in the journal Tobacco Control. While the danger smoke exposure poses to children's developing respiratory systems is well understood, less is known about its effects on overall infection risks.