ABC News' Mary Pflum and Bianna Golodryga report:
What do stars like Gwyneth Paltrow, Kim Kardashian and Oprah Winfrey all have in common?
Each is among the celebrities who have admitted to wearing Spanx and Spanx-like products, otherwise known as shapewear, to help flatten their tummies on walks down the red carpet.
The tight-fitting undergarments, which use Lycra and other form-fitting materials to cinch in the waist, are must-haves for millions of women longing to look more svelte.
But now the types of shapewear products that were developed with grown women in mind are attracting a much younger audience: teenagers.
"You get the training bra. You get the Spanx. Everyone wears them," 17-year-old Lindsey Luposello told " Good Morning America."
Teenage popstar Miley Cyrus wears them, and so do other teens as young as 13, all to make their waists look smaller and their bodies slimmer.
"GMA" sat down with a group of lacrosse players from Peekskill, N.Y., to discuss the growing trend. The girls, all ranging in age from 13 to 17, said they wear tight-fitting spandex shorts they like to called "spankies" both on the field and off. The shorts they wear are made by different designers. But all have one thing in common: the girls told "Good Morning America" that they hold their tummies in and make them feel less body-conscious.
"I wear them under everything, even to school," said 17-year-old Melissa Wagner, of the shorts, which work like Spanx. "You don't want people to see you have a muffin top."
Even thin girls, the lacrosse players said, are obsessed with tight-fitting Spankies.
"I feel like more and more skinny girls think that they're bigger than they are so they're having to hide something," said 14-year-old Stephanie Wagner.
Jill Zarin, a former cast member on the Bravo reality show " The Real Housewives of New York" who owns her own shapewear line, says she is not surprised by the growing interest of teens in shapewear. Zarin's 19-year-old daughter, Ally, started wearing shapewear at age 13.
"I'll probably be wearing it until I'm 63," said Ally. "Shapewear is the must-have accessory for every teenager starting in middle school, high school and throughout college."
Zarin developed her shapewear line, Skweez Couture, with teenagers in mind. The line features both grown-up pieces for moms -including luxe bustiers - and lacy biker shorts and camisole tops ideal for teens. Many of the teen-oriented pieces come in colors other than the traditional shapewear tones of nude and black tones - including pretty pastels, trimmed with lace.
"They have been selling like wildfire. I can't keep them in stock," she said of the line's pieces, which Zarin says has something for everyone. "Nobody wants to see anybody's body parts rippling. It's just not attractive."
The notion of teens wearing shapewear worries Dr. Orly Avitzur, a practicing neurologist and medical adviser to Consumer Reports.
"You are just squeezing the body too much so you are placing either direct pressure onto a nerve or squeezing internal organs," she said. "The tighter the fabric is or the more uncomfortable it is, the more likely you are to suffer damage."
Avitzur says she has treated 15-year-olds for shapewear-related problems which can include bladder infections, gastrointestinal problems and nerve damage that includes symptoms of numbness and burning in the thighs.
A spokesperson for Spanx told "Good Morning America" that, in the 12 years of doing business, Spanx has been unaware of customers suffering from nerve damage. "Our mission is to help women feel great about themselves and their potential," the spokesperson added.
But child psychiatrists like Dr. Ned Hallowell worries that teenagers obsessed with creating the illusion of a flat stomach are doing anything but feeling better about themselves - and are potentially setting themselves up for a host of psychological problems.
"The damage is eating disorders," said Dr. Hallowell, the founder of the Hallowell Centers in New York City and Sudbury, Mass. "The damage is never being happy with your body well into adulthood."
Zarin contends that teens who wear shapewear are being helped, not hurt, by their fashion choice. Shapewear, she says, can boost a young woman's self esteem and make a girl feel better about her figure.
"I think what shapewear does is sort of normalizes the girls' figures and evens everybody out," she said.
Zarin urges girls who find shapewear too tight or uncomfortable to try a looser style or to not wear it at all.
The teen girls "GMA" spoke with say that taking that advice is easier said than done since most of the girls they know would rather experience some shapewear-induced discomfort than be considered fat.
"When you feel the pain you say, 'It doesn't matter. All that matters is that I look good right now,'" said Stephanie Wagner.Also Read