On Tuesday, the U.S. Food and Drug Administration sent warning letters to 13 companies that appear to market their vaping products directly to kids. E-cigarettes are a gangbuster business but one device, the sleekly-designed Juul, has really captured the attention of underage teens. Vox’s Julia Belluz explains the hype, and what most teens don’t know about the Juul. Learn more about your ad choices. Visit podcastchoices.com/adchoices