Women have fought for decades to be treated as men's equals. Yet today's girls are being told that female empowerment simply comes from being 'sexy', according to a new book by the managing editor of the Harvard Law Review.

In Prude: How The Sex-Obsessed Culture Damages Girls, Carol Platt Liebau says popular culture is undermining girls' sense of worth in their most vulnerable, formative years and glorifying destructive behaviour .

'The overwhelming lesson teenagers are now learning from the world around them is that being "sexy" is the ultimate accolade, trumping intelligence, character and all other accomplishments at every stage of a woman's life,' said Liebau, a political analyst and the review's first female managing editor. 'The new female imperative is that it is only through promiscuity and sexual aggression that girls can achieve admiration and recognition.' She cites films such as Cruel Intentions and Mean Girls, the music and videos of Britney Spears, Christina Aguilera and Lil' Kim, and advertisements such as the dominatrix-themed campaign for the teenage fashion house bebe, featuring Mischa Barton. 'In a culture that celebrates Paris Hilton, thong underwear and songs like "My Humps" - where the female singer expounds the sexual magnetism of her breasts and buttocks - there's scant recognition or respect for female modesty or achievement that isn't coupled with sex appeal,' she adds.

'Girls are being led to believe they're in control when it comes to sexual relationships,' she continues. 'But they're actually living in a profoundly anti-feminist landscape where girls compete for attention on the basis of how much they are sexually willing to do for the boys.' Liebau's book has won support from feminists, including Ariel Levy, whose book Female Chauvinist Pigs denounced what Levy termed a 'raunch culture' that, she said, compels young women to 'compete to look like slags and sluts'. Although Levy was writing about women older than those concerning Liebau, she agrees that the age at which girls are being influenced by the raunch culture is falling. 'Even young girls are the willing, active and conscious participants in a tawdry, tarty, cartoon-like version of female sexuality,' she says.

In Prude, to be published in Britain by Centre Street Books this month, Liebau questions how society has created a climate in which being raunchy is believed to make girls look cool and in which being called a 'slut' is considered preferable to being labelled a 'prude'. 'By most measures, young women have never had it better. Given the breathtaking opportunities before them and the magnificent advantages they enjoy, it seems Western society has treated young girls with enormous generosity. And in many ways, it has. But not all the changes have been to the good,' she adds. 'Today girls are forced to navigate a minefield more challenging, difficult and pressure-filled than ever before when it comes to sex. Somehow, as society has been revelling the ubiquity of sex, the very real psychological, emotional and physical impact on young girls of giving too much, too soon, has been discounted,' she said.

Michele Elliott, director of the children's charity Kidscape, agrees. She has launched a campaign against the toy makers responsible for items including a junior pole-dancing kit, thongs for young girls emblazoned with the phrase 'Eye candy' and stationery sets stamped with the bunny logo of Hugh Hefner's Playboy empire.

In her book, Liebau charts how the same 'creeping sexualising' of young girls is endemic across a mass media which, she says, constitutes the main source of information about sex for 13 to 15-year-olds. 'Over the last few decades, the West has experienced an incremental but aggressive sexualising of its culture,' she says. 'Today there exists a status quo in which almost everything seems focused on what's going on "below the waist".'

Although her book has yet to be published in Britain, Liebau is keen to deflect any accusations of prudishness. 'This is about far more than short-term sexual mores,' she says. 'Living in an overly sexualised culture takes a toll on girls. The emphasis on sexiness, revealing fashions and the overvaluing of physical appeal creates pressure to measure up to bone-slim models or celebrities and leads to unrealistic expectations among young women about how their own bodies should actually look.'