NEW YORK -- "Small," reads the label dangling from the first tank top on the rack at the Brandy Melville store in SoHo. So does the one behind it. And the third, fourth, fifth -- they're all small. In fact, nearly every single piece of clothing in the store is either labeled "small" or "one-size."

Welcome to the hottest teen clothing retailer in the U.S., where the garments are designed for just one body type: thin. Brandy Melville has stormed onto the teen fashion scene with its "one-size-fits-most" policy and whimsical California vibe. Despite its modest fleet of 18 stores in the U.S., mostly in California and around New York City, it's one of the brands with the fastest-growing popularity among American teen girls, according to a semiannual survey from research firm Piper Jaffray.

Who is the Brandy Melville girl? One look at the brand's website and Instagram account reveals her: young, white, skinny and long-legged.

Typical Brandy Melville girls on Instagram.

"It's an exclusivity thing: Congratulations, you fit in the clothes! Join the club," said Justina Sharp, a 17-year-old fashion blogger who runs her style site, A Bent Piece of Wire. "There will always be the girls who will try to squeeze into it. They'll do whatever they can to fit in Brandy Melville."

While teens fawn over the retailer's assortment of crop tops, halters, cardigans and more, critics say Brandy Melville has raised the stakes when it comes to fat-shaming. Though the fashion world has long fetishized skinniness, and some labels cater to even slimmer profiles, few have taken size exclusivity this far. Yoga-wear company Lululemon, which admits plus-size customers aren't part of its strategy, does offer sizes from 0 to 12. Even Abercrombie & Fitch, derided for ignoring overweight kids, sells clothes with extra-large on the labels, up to size 14.

At Brandy Melville, nearly all the clothes are small, though a medium will pop up here and there. To be able to shimmy into Brandy Melville's only size of skinny jeans, a girl would need to have a 25-inch waist -- that's around a size 0 or 2, depending on the brand. Most skirts and shorts on the website are about the same size. Similar skinny jeans at teen fashion powerhouse Forever 21 span sizes from 24 to 30 inches. In the U.S., the average 16-year-old girl is approximately 5 feet 3inches tall, weighs about 138 pounds and has around a 31-inch waist, according to a 2012 report from the Centers for Disease Control and Prevention.

Brandy Melville is gaining traction with teens. (Data: Piper Jaffray)

Rachel Simmons, co-founder of the Girls Leadership Institute, a national nonprofit group, said Brandy Melville puts teen girls through the "paces of the popularity jungle," recreating the challenge of having to be the best and coolest in school.

Whereas typically teenage girls need to come up with the money to buy the "cool clothes," with Brandy Melville, cost isn't a challenge. The clothes are relatively affordable. Skirts and dresses run from $20 to $40. Plenty of tops cost less than $30, and some halters cost as little as $11.

With this label, cash is beside the point -- it's all about your body. That's an alarming message to put out to impressionable teenage girls, said Simmons.

"They're getting a really toxic message of what makes them worthy," she said. "All that matters is your body type."

The battle to be thinnest could be dangerous. A 2013 study from researchers at Texas A&M found that girls feel the most pressure to be skinny when they compare themselves with their peers. More than half of teenage girls use "unhealthy weight control behaviors," like skipping meals, fasting or vomiting, according to the National Association of Anorexia Nervosa and Associated Disorders.

Brandy Melville did not respond to requests for comment from HuffPost. But in an interview with USA Today earlier this year, Jessy Longo, an executive at Brandy Melville, addressed the one-size policy, saying that if customers can't fit in the clothes, at least they can buy an accessory.

"We can satisfy almost everybody, but not everybody," said Longo. "The one-size-fits-most clothing might turn off somebody if they don't walk into the store, but if you walk in you'll find something even if it's a bag."

Almost all of Brandy Melville's clothes come in "one-size-fits-most."

Founded in Italy by Silvio Marsan and his son Stephan as Brandy & Melville nearly two decades ago, the retailer came to the U.S. with little fanfare in 2009. Its first store opened adjacent to UCLA's campus in Westwood, Los Angeles. (The chain has 27 stores in Canada and Europe.)

Brandy Melville found its groove on Instagram, where its official account boasts more than 2 million followers. A look into the brand's Instagram approach by Racked revealed the retailer's "product research department" -- a corps of teens who fit the "Brandy Girl" image perfectly.

Regular teens aspire to one day be one of these Instagram girls, or at least look like them. Diehard fangirls treat the Brandy Melville girls like Internet celebrities, pinning Brandy Melville bags on their walls as decorations and Instagramming their caches of Brandy Melville clothes, explained Sharp. Teens will go to a Brandy Melville store just to take a selfie and share it, she said.

Since its arrival on the West Coast, Brandy Melville's clothes have swept through high schools, attracting teen girls who want to be part of the waif club. Lani Renaldo, a freshman at the University of Southern California who graduated from a Santa Monica high school in the spring, said Brandy Melville clothes were unavoidable among teens in the area. They became necessities, she said.

"It was really uncommon to know somebody who didn't have Brandy Melville," Renaldo, who wrote a blog post earlier this year condemning Brandy Melville for leaving teens as outcasts, told HuffPost. "You had to own something from Brandy, and if you didn't, it's really weird."

Inside the Brandy Melville store in SoHo, New York City. (Photo Credit: Kim Bhasin/The Huffington Post)

With all the importance it places on teensy waists and thigh gaps, the Brandy Melville culture was bound to court controversy.

In 2012, YouTube star Trisha Paytas said she'd been shamed at a Brandy Melville store in California. In a video uploaded to her YouTube account, Paytas alleged that a store employee wouldn't even let her try on clothes because of her size. She said she took down the video after receiving a letter from a lawyer representing Brandy Melville.

Paytas described the experience in an email to Brandy Melville: "I didn't get 10 seconds into the store when I was told 'I would not fit anything' and that I wasn't allowed to try anything on because 'I would stretch the clothes out.'" She added that many of her viewers have had similar experiences at Brandy Melville shops. Paytas declined an interview request for "legal reasons."

Whether fat-shamed directly or not, it's evident that Brandy Melville customers feel the pressure, even by simply walking into a store. Take this sampling of customers lamenting their weight because of Brandy Melville:

how to feel fat: brandy melville jeans — layn (@yunglaynr) September 27, 2014

I would buy stuff from Brandy Melville but im too fat. — ericka (@damnbehlendorf) October 13, 2014

crying bc too fat to fit into brandy melville.. sigh — kelly may // 9 (@viralmcvey) August 4, 2014