It's official: sexualisation harms girls. Of course it does. It harms all of us. It doesn't just make girls ill, it harms boys too, teaching them to be sexually violent.

The American Psychological Association's findings - that the portrayal of girls and young women as sex objects harms girls' mental and physical health - should be addressed at the root cause: the media. Powerful and profit driven, they are left to self-regulate with their own voluntary codes. Not only is this not working, it's harming society. The Government needs to introduce responsible media regulation, in which social responsibility and harm are not compromised for free speech. Only then will we see diverse representations of females in positive roles.

As a society, we should be extremely worried. The saturation of sexualised images of females is leading to body hatred, eating disorders, low self-esteem, depression, high rates of teen pregnancy and unhealthy sexual development in our girl children. It also leads to impaired cognitive performance. In short, if we tell girls that looking "hot" is the only way to be validated, rather than encouraging them to be active players in the world, they underperform at everything else.

But the consequences of sexualising girls are far more devastating than this. Rape is at crisis levels, and one in three women will be a victim of stalking, sexual harassment or sexual violence in their lifetime.

But who are the mysterious perpetrators of these crimes? Much of the media, the justice system and one-third of the public seem to think alcohol is raping girls. That by getting drunk, dressing sexy and flirting, girls and women are responsible for the horrific violence committed against them.

Only 8 per cent of rapes are stranger rapes. It is ordinary boys and men who are committing these sexually violent crimes against girls and women. It is appalling that when another rape or sexually violent crime is reported on the news - so ubiquitous it is unremarkable - it is never followed by a report asking: "Why are boys and men sexually abusing and raping girls and women? Where do they learn to film this abuse on their mobiles? Where do boys and men learn that having power over women and being violent is an acceptable way to be a man?" Instead, the onus is on girls and women to curb their behaviour and lives.

The sexualisation of girls and the normalisation of the sex and porn industries have made it increasingly acceptable and "fun" for women to be viewed as sex objects, and for men to view women as sexual commodities. To speak out against this trend is framed as "anti-fun" and "anti-sex". The pressure group Object has documented how men's "lifestyle" magazines and lad mags do not merely objectify women, they trivialise trafficking, sex tourism and prostitution. The number of young British men using prostitutes has doubled in a decade to one in 10 in 2000.

The charity the Lilith project has found that the increasingly mainstream pole- and lap-dancing and porn industries are careful to hide their links with prostitution, trafficking and sexual violence. A five-year-old boy can buy a lad mag and learn that women are only sex objects and he has entitlements to their bodies. If he logs on to Zoo magazine's website, he can watch videos of girls stripping and lap-dancing, one set up as if the woman is being stalked and secretly filmed in her bedroom while she strips, another of a "ridiculously hot" girl being so frightened, she is screaming and crying uncontrollably in a ball. This is not just about sexualisation. Sexual harassment is being eroticised.

The sexualisation of girls exploits girls and boys. All children and young people are under immense pressure to accept it. Boys who are not enthusiastic about it, or speak out against it, run the risk of being ignored or ridiculed, of being labelled "gay", "unmanly", or not liking sex. Boys and young men are under pressure to act out masculinity in which power and control over women, and men, is normal. In which violence is normal.

The absence of positive role models in boys' immediate lives is showing. If the adult men around them do not challenge sexism and traditional masculine behaviours, boys won't either. And with absent fathers, boys are left with celebrities and sports heroes to look up to. Music videos largely follow a template of an individual man possessing a group of sexualised women, gangsta rappers promote sexist and violent notions of masculinity, many young footballers and other sportsmen behave like playboys, enjoy group sex, get away with rape and keep their "hero" status.

Damian Carnell who works to prevent anti-gender violence, says: "From boyhood, men read into the messages that we see around us, from men's institutionalised superiority over women, and privileges of being male, to negative stereotypes of girls and women. It's no wonder that 35 per cent of boys aged 11-16 believe it is justified to abuse women."

The sexualisation of girls is not just shattering the lives of girls and women, it is preventing boys and young men from relating to girls and women as complex human beings with so much to offer them. It is preventing boys from forming healthy friendships and working relationships with girls and women. Instead, it is nurturing potentially violent abusers, rapists and johns. Ultimately, it means boys are not free to be themselves, to know their own humanity.