The Centers for Disease Control and Prevention says it's worried about the amount of second-hand smoke being inhaled by teens and middle-schoolers in cars.

In the first national estimate of its kind, a report from government researchers says more than 1 in 5 high school students and middle schoolers ride in cars while others are smoking.

The report says this kind of secondhand smoke exposure has been linked with breathing problems and allergy symptoms, and more restrictions are needed to prevent it.

The CDC says there is no risk-free level of secondhand smoke.

With widespread crackdowns on smoking in public, private places including homes and cars are where people encounter secondhand smoke these days. Anti-smoking advocates have zeroed in on cars because of research showing they're potentially more dangerous than smoke-filled bars and other less confined areas.

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