Young women who have been sexually abused are a lot more likely to become sexually active. For young men, their strongest trigger is pornography.
Young men who had watched pornography were about six times more likely than those who did not do so to have sex, according to a local study.
Associate Professor Wong Mee Lian, who led the study, explained: "They see others having so much pleasure and they want to try it too. At their age, they lack impulse control and they have a heightened need for sensation seeking."
For young women, those who had been sexually abused were about eight times more likely to subsequently have sex voluntarily. They also had more sexual partners, an average of seven by the time they were interviewed for the study, compared with the average of four for girls who had not suffered abuse.
Prof Wong, who is from the Saw Swee Hock School of Public Health at the National University of Singapore, said: "Overseas experts have explained that a teenage girl who was abused might find it difficult to recognise she has a right to her own boundaries and to impose limits on sexual advances." She said another theory states that the girls may be led to think their self-worth is tied to being sexually available.
For the study, she and her team interviewed 1,000 young people aged between 14 and 19. Half were sexually active and new patients at the Department of SexualIy Transmitted Infections Control Clinic. The other half were virgins.
The study was published in Pediatrics, a medical journal, in 2009. Besides Prof Wong, the co-authors were Adjunct Professor Roy Chan, Professor David Koh, Dr Tan Hiok Hee, Dr Lim Fong Seng, Dr Shanta Emmanuel and Professor George Bishop.
She said that a significantly higher proportion of both the young men and women who had premarital sex lived in smaller flats (one- to three-room flats), had dropped out of school or had divorced parents. Those who lacked confidence to resist peer pressure were also more likely to have sex.
Social workers, commenting on the finding that those who live in smaller flats or had divorced parents were more likely to have premarital sex, stressed the importance of parental guidance in young people's growing-up years, lest they fall into the wrong crowd.
Ms Lena Teo of the Children-At-Risk Empowerment Association said: "The young need parents who express their love and care and are there for them in critical moments of their lives."