Last week the FDA bequeathed its coveted approval to Kybella, an injectable drug that promises to melt away chin fat. That’s right—a double-chin eraser that comes in a syringe.

Until now those who wanted to reduce a double chin (medically known as "submental fullness") would have to undergo liposuction—which, as a surgical procedure, is somewhat invasive and requires a few days of recovery. So a nonsurgical fat melter is a pretty big deal.

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But how does it work, exactly? And will it blast other types of fat? (Asking for a friend.) We answer all your burning questions about the injection below.

First things first, what is in that needle?

Kybella is the trade name for ATX-101, a patented synthetic form of deoxycholic acid, a naturally occurring molecule that helps metabolize dietary fat.

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The drug was created by Kythera Biopharmaceuticals, a California-based company that focuses on prescription cosmetic products.

Does it really “melt” away a double chin?  

Well, it’s not like putting a stick of butter in the microwave. More like bursting a liquid butter-filled water balloon with acid. But let's have someone else explain.

Derek H. Jones, clinical associate professor of dermatology at UCLA and lead clinical investigator of Kybella, spoke with Fusion about what ATX-101 is and how it works.

“Basically, what it’s doing is disrupting the fat cell membrane,” Jones said. “As soon as it hits, it causes lysis—or destroys the cell membrane. After that, the fat cell releases its fatty contents and the body metabolizes the fatty contents as normal.”

So you’re popping fatty cells? Whose idea was this, anyway?

While Kybella is the first FDA-approved fat-zapping injection in this country, the concept has existed outside the U.S. for decades.

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Zakia Rahman, clinical assistant professor of dermatology at Stanford, told Fusion: “The whole idea of doing these injections was initially pioneered in France, with a few people making their own cocktails and injecting them, many with adverse effects.” Naturally.

Until Kybella, the FDA cautioned consumers against injections meant to "dissolve and permanently remove fat." Along with deoxycholic acid (the same used in Kybella), these injectable concoctions often contained other acids and even herbal extracts. None of the injections had undergone clinical trials or presented evidence of effectiveness.

So the fact that Kybella actually scored the approval from the FDA is a very notable breakthrough, according to Rahman. “The results are actually quite impressive,” she told us.

Who will administer it?

Trained professionals, that’s who. As the FDA stipulates, Kybella treatments “should only be provided by a licensed health care professional.” Jones will be training professionals himself, starting in June. Kythera has not disclosed exactly who they will be training.

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Rahman told Fusion that Kythera will likely train dermatologists and plastic surgeons, but warned that, as with any cosmetic procedure, the consumer should be cautious about who is administering Kybella—doctors without proper expertise may offer the drug.

“A doctor might be board certified, but it could be in internal medicine," Rahman said. "The consumer has to be aware, which is difficult."

So can anyone go and get this?

Almost. The drug is not approved for kids under the age of 18. Kythera also recommends that doctors screen patients carefully to make sure that their submental fullness is indeed fat and not the result of something else, such as thyromegaly (enlargement of the thyroid) or cervical lymphadenopathy (enlargement of cervical lymph nodes in the neck).

What happens to excess skin once the fat dissolves?

If doctors are detonating fat in your chin and the fat disappears, that leaves you with some leftover skin, right? Well, technically, that risk exists with lipo as well. For lipo patients with particularly elastic skin tone, the loose skin is not that noticeable after a few months. But for others, it is—and chin or neck liposuction is often paired with a neck-lift surgery.

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Doctors administering Kybella are advised to screen for patients who have excessive skin in the chin area or “other conditions for which reduction of submental fat may result in an aesthetically undesirable outcome."

As for the recovery itself, "There is an inflammatory component immediately after the injection," Jones told Fusion. "There is some swelling and some tenderness for a few days because the body is cleaning up all cellular debris and creating a bit of contraction in the skin." But because it's not an invasive procedure, the recovery promises to be faster than recovery from liposuction.

Huh. So can you just stick that needle anywhere and melt away other fatty areas?

Um, no. First of all, ATX-101 is only approved for the chin area—and it must be applied extremely skillfully. If a doctor were to hit the marginal mandibular branch of the facial nerve, the patient could end up with an asymmetrical smile. If the doc doesn’t insert the needle deep enough, it could cause skin ulceration. Hence the required training.

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Rahman also cautioned that if a patient's main concern is weight loss, he or she shouldn't rely on surgeries and cosmetic procedures. “We do have an epidemic of obesity and people want to find a way to lose the fat, but really, the only way to treat obesity is mainly through diet and exercise,” she said. “Doing this procedure is not a way to lose weight."

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Rahman added that she makes sure her patients understand the value of restraint when it comes to aesthetic procedures: “It’s important to balance the desire to look one’s best with that pressure to look perfect.”