WALNUT CREEK, Calif. -- If you can stand straight with your knees together and see a space between your upper thighs, you have what thousands of teen girls are willing to starve themselves for.
The thigh gap, as it is known, is a small, hollow cavity with a huge following on social media. You can follow supermodel Cara Delevingne's thigh gap on Twitter or peruse thousands of thigh gaps on Tumblr with images of ultrathin women in bikinis, hiked up skirts, and lingerie, all baring thighs so thin they don't touch. The photos come with captions like, "Three more inches to go" and "All I want in life is a thigh gap."
Women have long been bombarded with unrealistic images of beauty and digitally altered bodies. But the thigh gap is the first "thinspiration" voice in social media, where sharing with friends spreads and fuels the obsession.
The thigh gap's social media presence is, in fact, a "perfect storm," says Berkeley, Calif., licensed clinical social worker Debra Milinsky of the Feminist Therapy Connection.
"Girls are at a developmental stage where their bodies are changing, and when it comes to what they're supposed to look like, they're most likely to listen to their peers," Milinsky says. "That's what the Internet is all about. Seeking community."
Of course, not all girls want to join that particular one. Maya Sweedler of Los Gatos, Calif., calls the thigh gap trend "awful."
"I can't believe what some girls are encouraging each other to do, to be so unhealthy and all look the same," says Sweedler, 16.
Any number of factors play into whether a woman has a significant thigh gap, including genetics, ethnicity, pelvic size and width, says Laura Tosi, a pediatric orthopedist and director of the bone health program at Children's National Medical Center in Washington, D.C.
"Weight loss is proportional, so most girls who don't have a natural gap -- one bigger than a peephole -- would have to lose a lot of weight to achieve the kind of thighs coveted on social media," she says.
"Weight gain is actually a natural and very important signal that a young woman is entering womanhood and starting her periods," Tosi explains. "Delaying the onset of menses by severe weight loss can impair a young's woman's skeletal development and lead to fractures even as a young adult."
Try telling that to an impressionable girl who has consumed unattainable images of beauty since age five, says Lucie Hemmen, a Santa Cruz, Calif., psychologist and author of Parenting a Teen Girl: A Crash Course on Conflict, Communication, and Connection with Your Teen Daughter (New Harbinger, $20).
"That's how early girls fall prey to this issue," says Hemmen, who is the mother of two girls. "I feel like thigh gap is just the newest incarnation of a ridiculous standard that's depicted in the media. It used to be a concave stomach. Next, it'll be a dimple here or there."
To combat the spread of thigh gap worship, Hemmen says parents must teach their daughters media literacy and hang around when their teenager is trawling Tumblr or watching a YouTube video so they can say, "Honey, that's been digitally enhanced. No one looks like that."
"We need to encourage irreverence in girls about a media that doesn't give an (expletive) about their health and wellness," she says.
Meanwhile, a small, anti-thigh-gap movement is developing online. Tumblrs like Touching Thighs and No Thigh Gap give Hemmen hope, she says. They also remind her how much teenagers love to push back against the status quo.
-- MCT Information Services