A review of research has revealed striking similarities in the influences on young people's sexual behaviour across the world.

The review of qualitative studies, published today in The Lancet, looked at 268 studies of the sexual behaviour of under-25-year-olds from South Africa to Sweden. It reveals how, in all countries, social expectations of how men and women should behave frustrate campaigners' efforts to encourage safer sex.

For example the review found young women often feel their reputation will be sullied if they carry condoms, and young men often feel pressured into having sex when they get the opportunity, whether they have a condom or not. It also found that young people around the world find it hard to even discuss the possibility of sex with potential partners, which makes it difficult to plan condom use.

Other common themes included, for example, a tendency to try and guess the HIV status of potential partners using unreliable indicators such as an individual's appearance, or how well they know them. Young people are less likely to use condoms if they guess that the partner is 'clean'.

Dr. Cicely Marston, of LSHTM, who led the review, said it showed why many campaigns to encourage safer sex had failed. 'Our findings help to explain why many HIV programmes have not been effective', she said. 'Giving out condoms and information is vital, but it is not enough. Even where young people know about the importance of condoms, social factors in particular stereotypes about how men and women should behave and a reluctance to talk openly about sex hamper their use. Safer sex campaigns need to tackle these issues if they are to succeed'.