The Centers for Disease Control and Prevention say about 2.4 million students in middle school or high school have used e-cigarettes.

According to the CDC, more than 18 million students saw ads for e-cigarettes. Their report says more than one in two were exposed to ads in retail stores, and about two in five teens saw e-cigarette ads online.

Patricia Folan, the director of the Center for Tobacco Control, says with more than 7,000 flavors, the perception is e-cigarettes are less harmful. She says while the safety and effectiveness have not been determined, there are side effects to their usage.

"They contain nicotine, which is damaging to the developing brain of a teenager. It can lead to addiction and then lifelong use of tobacco," says Folan.

The FDA has not yet regulated e-cigarettes.