Second hand smoke causes permanent damage to kids' arteries.

"Passive smoking" prematurely ages a child's blood vessels by more than three years, according to a new study of more than 2000 children from ages 3 to 18.

That damage thickens the blood vessel walls and increases the risk of heart attacks and strokes in later life.

Ultrasound scans showed how kids whose parents both smoked developed changes in the wall of a main artery that runs up the neck to the head. Those changes were detectable 20 years later.

The study's authors conclude there is NO safe level of exposure to second-hand smoke for kids.

--Rob Archer