Scientists are pretty much in agreement that at least half of your personality comes from your gene pool—it's part of the identity card you're issued at birth. Life experiences help to shape the other half. If you acquire some idea about yourself—perhaps you're known as the problem child in a classroom or the slacker in a family—that idea will have an impact on your brain circuitry and get built into how you think about yourself. "Our human brains love to categorize and label—'the pretty one' or 'the dependable one' or 'the smart one,'" says Brizendine. "Then you grow accustomed to the label and often re-create that identity because it feels familiar. It can mean all kinds of goodies but also all kinds of burdens."

The only time I go into Old Navy is when I need a teen-appropriate gift. (I generally have a rule: If I can't stand the store's music, I'm too old to wear the store's clothes.) But recently I was seduced into the dressing room by the lure of cool cheap stuff and found a virtual petri dish of youthful vulnerability about believing the bad stuff—I eavesdropped on one plaintive "Does this make me look fat?" after another. "One of the major tasks of adolescence is, 'Who are you?'" says Jessica Henderson Daniel, PhD, associate professor of psychology at Harvard Medical School. "Belonging and finding your niche in terms of assets and liabilities is colored by what other people see—because you don't live in a bubble. More often than not, girls don't look like what they think they should look like." There is a critical window of opportunity in early childhood when it is possible to infuse a girl with a sense of self-worth that is not based on the size of her breasts or the luster of her hair, says Daniel. "People generally fall short of the media ideal, which is why I advocate helping youngsters prepare for adolescence in their elementary years, building up their skills so they have proof that they are more than an image. Youngsters who have pride in accomplishment are more anchored."

A study at the University of Texas how easily body image is undermined: A group of adolescent girls were in a room with an attractive woman who complained about how fat she was (the implication being that anybody who was heavier than she would really have something to complain about). There was an immediate impact on the body image of the girls, even though the encounter was brief and the woman was a stranger. "Up to 50 percent of adolescent girls have body image concerns," says Eric Stice, PhD, lead researcher on that study. "Up to 70 percent of girls say they would take a pill to lose five pounds; with males, it's maybe 15 percent. And puberty moves young men toward the ideal male body image, strong and muscled, but moves young women away from the ideal female body image, lean with no hips. It's really sad that adolescent girls look at airbrushed images in the media that aren't even real. They're killing themselves for something that isn't real."

From the August 2008 issue of O, The Oprah Magazine

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