DENVER — Serenity Christensen, 14, is too young to set foot in one of Colorado’s many marijuana shops, but she was able to spot a business opportunity in legal weed. She is a Girl Scout, and this year, she and her mother decided to sell their cookies outside a dispensary. “Good business,” Serenity said. But on the other side of Denver, legalization has turned another high school student, David Perez, against the warehouselike marijuana cultivations now clustered around his ne

People have been smoking for at least 7,000 years, but it wasn't until the 1800s that cigarettes became the smoke of choice, after machines were developed to mass produce them. 200 years later, in 2003, the electronic cigarette was invented in China. Since then, the use of e-cigarettes, also known as vaping, has grown exponentially around the world. Source: David Geffen School of Medicine UCLA