Children exposed to sex in TV programmes, films, magazines and music are more likely to engage in sexual activity than those who are not, according to research out yesterday.
There is a direct relationship between the amount of sexual content a child sees and their level of sexual activity or their intentions to have sex in the future, the study found.
Such media also has at least an equal influence on sexual behaviour as religion or a child's relationship with their parents and peers, the study said.
It concluded that the media is an "important source" of information about sex for teenagers who might not get advice elsewhere.
More than 1,000 American children aged between 12 and 15 were asked to identify from a huge list the kinds of media they were exposed to.
They also answered questions about their health and levels of sexual activity, including whether they went on dates, kissed, had oral sex or full sex.
Researchers then examined the sexual content of 264 items on the list, which included teen magazines, teen movies and TV programmes.
They looked for examples of romantic relationships, nudity, sexual innuendo, touching, kissing, puberty and sexual intercourse.
The study, published in the Journal of Adolescent Health and in Elsevier, found that films, TV programmes, music and magazines usually portrayed sex as "risk-free".
Sex was usually between unmarried couples and examples of using condoms or other contraception were "extremely rare".
The study concluded: "The strong relationship between media and adolescents' sexual expression may be due to the media's role as an important source of sexual socialisation.
"Adolescence is a develop-mental period that is characterised by intense information-seeking, especially about adult roles, and given the lack of information about sexuality readily available to teens, adolescents may turn to the media for information about sexual norms."
The researchers said the media may serve as a kind of "sexual super peer" for teenagers seeking information about sex.
* The average age of the children was 13.7 years, with about one third thought to come from poorer backgrounds, receiving free or reduced price school meals.