Juul looks like a sleek USB flash drive, its flavor pods are packed with nicotine and it is the latest trend in e-cigarettes.

In the past year, San Francisco-based Juul Labs has rapidly overtaken the U.S. e-cigarette market. Sales have skyrocketed nearly 800 percent, helping Juul capture a 71 percent of share of the market, according to Nielsen data. Juul's rise has attracted venture funds and given it a stunning $15 billion valuation. But this explosive growth has drawn scrutiny. The company faces lawsuits and FDA regulation, and its popularity among teens could threaten its future.