As if there wasn’t already enough to worry about when your kids are riding around in cars — texting, speeding, distracted drivers, drunk drivers, etc. — add this one to your list: secondhand smoke. A new study released today by the Centers for Disease Control and Prevention (CDC) says that way too many kids are exposed to secondhand smoke in cars. And it’s not always from parents or other adults as many middle schoolers and high schoolers report riding in the car with friends who smoke.In many areas, smoking in public places has become taboo or even illegal, so smokers have retreated to their homes and cars to light up. But smoking in cars is particularly dangerous because of the enclosed conditions of the vehicle. And no, rolling the window down doesn’t help. Secondhand smoke exposure has been linked with breathing problems and allergy symptoms. Secondhand smoke exposure in cars ups the risks exponentially. According to the CDC, more restrictions are needed to prevent kids from being exposed to secondhand smoke.The new report from the CDC found that more than 1 in 5 high school students and middle schoolers reported riding in cars while others are smoking. When asked how often they rode in cars with smokers, the most common answer was once or twice a week.Overall, 22 percent of teens and pre-teens were exposed to secondhand smoke in cars in 2009, the latest data available. That figure has declined significantly from 40 percent in 2000, but still, “there is no risk-free level of exposure to secondhand smoke,” the CDC says.   There are currently fours states (Arkansas, California, Louisiana and Maine) as well as Puerto Rico that have “smoke-free car” laws prohibiting adults from smoking in a car while children are present. And according to the CDC report, more states need to enact this type of legislation to protect kids from secondhand smoke exposure in cars.MORE FROM MOTHER NATURE NETWORK: Father’s Smoking Linked to Child’s LeukemiaBans Mean Less Smoking in HomesDriving Stoned: What Can Happen