The demonisation of teenage girls by the media is allowing suspected rapists to escape prosecution, according to the head of the Crown Prosecution Service in London.
Alison Saunders has warned common myths about young women in the media are affecting how jurors consider evidence in rape and sexual assault trials.
Some victims are not even reporting crimes because they fear they will be vilified, she added.
In an interview with the Guardian, Saunders called for more to be done to challenge peoples' negative preconceptions of young females before they enter court.
"If a girl goes out and gets drunk and falls over they are almost demonised in the media, and if they then become a victim, you can see how juries would bring their preconceptions to bear," she said.
"The majority of victims are under 18, a lot have drink or alcohol involved, some are repeat victims. If she has been a repeat victim, do you believe her, or is this something about her or about the defendant?
"We need to encourage people to come forward so it is not something you will be vilified for, and jurors, when they come to cases, they come with a genuinely open mind without any preconceptions."
Saunders said prosecutors and detectives involved in rape cases were trained to challenge myths and stereotypes, but argued a wider debate on the issue with "government publicity or government guidance" was needed.
The prosecutor added: "We have done lots of training, but there has never been that debate on a wider social basis. You can see how some members of the jury can come along with preconceived ideas, they might still subscribe to the myths and stereotypes that we have all had a go at busting."
Saunders said judges give advice and directions during a trial, but it often comes too late to make jurors think twice.
"There have been a lot of developments about what judges can say to jurors," she said.
"Judges cannot do rape cases unless they are specialists and they have been through the myth-busting courses.
"But my view is that sometimes it is possibly too late. You may have someone who has already listened to the evidence and may have made up their mind."
The London division of the CPS is the largest in England and Wales and last year considered 870 suspected rapes, sending half to trial. Of those, just over 50% ended up with convictions.