Young people who rely on their friends for information about sex are significantly more likely to have sex earlier, while relying on a teacher as a source of information on sex and relationships is associated with later sexual initiation.
The finding is among a number contained in two studies into young people and sexual health and knowledge carried out by the ESRI and funded by the HSE.
One of the studies also finds low levels of knowledge around fertility issues among young people and finds that young people who had received Relationships and Sexuality Education in school or spoke with their parents about sex and relationships did not have a greater level of knowledge.
The two studies are based on data gathered under the 'Growing Up in Ireland' programme which is tracking a large number of nationally-representative young people who were all born in 1998.
The data was gathered from the young people in 2018 when they were 20 years of age, and prior to the introduction of a new Social Personal and Health Education programme at Junior Cycle level.
The report 'Sexual Initiation and Sexual Health Behaviours among Young Adults in Ireland' examined the factors associated with the timing, and circumstances, of first sex.
It found that just over one-third of males and females first had sex by the age of 17, while a further 50% sex before the age of 20. The remaining 15% had not had sex by the age of 20.
It also found that having a larger and more age diverse peer network as well as acquaintances who were themselves having sex meant a young person was significantly more likely to have sex earlier.
A second report 'Sexual Health Literacy and Sexual Health Behaviours among Young Adults in Ireland' examined the factors associated with sexual health literacy among young people, and condom and contraception use for those currently having sex.
It found knowledge that condoms are the best method for the prevention of sexually transmitted infections (STIs) was high but that knowledge of fertility, and specifically the period during the female menstrual cycle when pregnancy is most likely to occur, is much lower, with just one in five young men, and 37% of women, answering correctly.
"Low levels of fertility knowledge among women and men, which have implications for their future pregnancy planning, point to the need for this issue to be addressed through the revised RSE curriculum, underpinned by ongoing professional development for teachers and supports for parents to engage in conversations about sex with their children," one of the report's authors Professor Emer Smyth said.
This second study found low levels of condom use and a decline in contraception use between first and current sex, which point to the need for renewed public health communication, the study says.
"Sexual health literacy is not sufficient to ensure safe sexual behaviours among young adults but needs to be underpinned by a multi-pronged approach involving parents, peers, schools, youth clubs, public health professionals and other service providers," the report's authors concluded.
The research also found that existing RSE provision in schools had not provided an adequate knowledge base on fertility.
"Those who had received relationships and sexuality education (RSE) at school, and/or had discussed sex and relationships with their parents, were not more likely to answer the sexual health literacy questions correctly."
An updated junior cycle SPHE course, which includes RSE, has been in place since September 2023, while a new senior cycle curriculum is currently being rolled out and must be in place in all schools from September 2027.
The report’s authors have said that ongoing training for teachers is crucial in order to support the new programmes.
"It is crucial to build upon existing continuous professional development, including the recent graduate diploma in SPHE/RSE, to enhance teacher confidence in ensuring increased knowledge of fertility among future cohorts of young people," the report states.
The report 'Sexual Initiation and Sexual Health Behaviours among Young Adults in Ireland' also found that young women were significantly more likely to express regret over the timing of first sex than young men.
A quarter of young women thought that it had happened 'too soon', compared to 10% of young men.
Those who had sex for the first time later were less likely to think that their first sex had occurred 'too soon'.
"Along with recent rises in STI notifications among young people in Ireland, the findings in relation to condom use highlight the need for renewed public health messaging about the benefits of condoms in preventing both pregnancy and STIs," report author Professor Anne Nolan said.
