Second-hand tobacco smoke may pose more of a heart risk to teenage girls than boys, research suggests.
Scientists found that girls exposed to other people's smoke at home had reduced levels of the "good" cholesterol that protects arteries.
However, the same effect was not seen in boys.
"Good" cholesterol, or high-density lipoprotein (HDL), helps reduce heart disease, unlike the "bad" form of cholesterol, low-density lipoprotein (LDL).
Molecules of HDL pick up excess cholesterol in the blood stream and carry it to the liver where it is broken down.
In contrast, LDL contributes to hard deposits that build up on artery walls impeding blood flow.
Lead researcher Dr Chi Le-Ha, from the University of Western Australia, said: "In our study, we found 17-year-old girls raised in households where passive smoking occurred were more likely to experience declines in HDL cholesterol levels.
"Second-hand smoke did not have the same impact on teenage boys of the same age, which suggests passive smoking exposure may be more harmful to girls. Considering cardiovascular disease is the leading cause of death in women in the western world, this is a serious concern."
The scientists looked at data on more than 1,000 adolescents born between 1989 and 1992 in Perth, Australia.
Information was collected about smoking in the household from the 18th week of a mother's pregnancy to when her child was aged 17.
During that time, 48% of participants were exposed to second-hand smoke at home.
Blood tests were carried out to measure the teenagers' cholesterol levels.
The results are published in the Journal of Clinical Endocrinology & Metabolism (JCEM).
"The findings indicate childhood passive smoke exposure may be a more significant cardiovascular risk factor for women than men," said Dr Le-Ha. "We need to redouble public health efforts to reduce young children's second-hand smoke exposure in the home, particularly girls' exposure."