WASHINGTON (AP) — Hundreds of electronic cigarette brands will have to get federal permission to stay on the market under new rules that have the potential to upend a multi-billion dollar industry.

The Food and Drug Administration has released long-awaited rules that bring the industry under federal oversight. Among other steps, the FDA rules limit e-cigarette sales to minors and require new health warnings. In a move vigorously opposed by manufacturers, the agency says manufacturers would have to get permission to remain on the market under a multi-tiered system.

E-cigarettes turn nicotine into an inhalable liquid vapor. Their benefits and harms haven't been extensively studied.

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WHAT DID THE FDA DO?

It finalized a rule extending its authority to all tobacco products, including electronic nicotine delivery systems like e-cigarettes and vape pens, as well as hookah tobacco and other items.

Hundreds of e-cigarette brands will have to undergo a lengthy review to stay on the market. The government also will limit e-cigarette sales to minors and require new health warnings.

- WHAT ARE ELECTRONIC CIGARETTES AND WHO USES THEM?

E-cigarettes are battery-powered devices that turn liquid nicotine into an inhalable vapor.

More than 15 percent of high school students report using e-cigarettes, up more than 900 percent over the last five years, according to federal figures.

More than 12 percent of adults have tried them.

- HOW BIG IS THIS MARKET?

Wells Fargo Securities analyst Bonnie Herzog estimates that the total vapor market will reach $4.1 billion this year, with e-cigarettes accounting for $1.6 billion of that total.

- WHAT'S THE HARM WITH ELECTRONIC NICOTINE DELIVERY SYSTEMS?

Nicotine is addictive and can impair the brain and lung development of fetuses, the Centers for Disease Control and Prevention has noted. It also can disrupt the formation of brain circuits in adolescents that control attention, learning and addiction susceptibility.