Never having had a girlfriend, or one who is sexually active, and watching pornography frequently are the two strongest reasons why teenage boys turn to prostitutes, according to the first study here on teens who pay for sex.

Other reasons that some boys are more likely than others to visit prostitutes include the fact that they started having sex before the age of 16, said Associate Professor Wong Mee Lian of the Saw Swee Hock School of Public Health at the National University of Singapore, who led the study.

They could have reached puberty earlier and tend to have older friends who exposed them to behaviour that included smoking, drinking and sex with prostitutes, she said.

Another factor is that these teens have lower self-esteem.

"These boys want to feel accepted and want to boost their ego. They may not have a girlfriend to boast of, but they can pay to 'conquer' a prostitute," she added.

SUCCUMBING TO PEER PRESSURE The boys say their friends dare or urge them to go to a sex worker to initiate them into manhood. '' ASSOCIATE PROFESSOR WONG MEE LIAN SEX ON THE CARDS The holidays are to chill and to drink, not specifically to have sex. But when it's all boys going on holiday, sex somehow becomes part of the package. '' ADRIAN (not his real name), on his overseas outings with his friends.

Her study found that educational background or the type of home the family lived in was not a factor in whether a boy was more likely to go to a prostitute.

Prof Wong and PhD student Junice Ng studied 300 heterosexual boys aged between 16 and 19 who visited the Department of Sexually Transmitted Infections Control (DSC) Clinic between 2009 and 2014. The government clinic focuses on the treatment of sexually transmitted infections (STI).

The researchers noticed that more young patients at the DSC clinic said that they have had sex with a prostitute in recent years.

So, they decided to find out more.

Their research, published in the science and medical journal PLOS One in January, found that 39 per cent of the boys polled said they had sex with prostitutes - a figure that Prof Wong described as high.

According to the study, of the boys who visited prostitutes:

• The median age was 16.

• It was the first sexual experience for 38 per cent of them.

• They had a median number of 4.5 sexual partners, including girlfriends or casual friends they slept with, by the time they were interviewed by Prof Wong's team.

• 30 per cent did not use a condom consistently, that is, each time they had sex with a prostitute.

• 42 per cent were diagnosed with an STI, but none was infected with the Human Immunodeficiency Virus (HIV) that causes Aids.

• Those who did not use condoms consistently were a lot more likely to be diagnosed with an STI.

Prof Wong said the teens' multiple partners and inconsistent condom use are a concern. They could be infected with an STI and pass it on to their girlfriends or others they have sex with.

Related Story More teenage boys paying for sex: Study

Doctors and social workers said peer influence and pressure, plus curiosity about sex or a desire to be seen as sexually experienced, are also reasons why the teens turn to paid sex. Prof Wong said: "The boys say their friends dare or urge them to go to a sex worker to initiate them into manhood."

Those interviewed said national service is one stage in life where many young men get introduced to paid sex by their more sexually experienced mates. Take, for example, full-time national serviceman Raymond (not his real name), who had his first sexual encounter with a prostitute last year when he was 18.

"My army mates talk openly about their sexual experiences and visiting prostitutes. And if you have nothing to share, they tease you," the 19-year-old said. "I was a bit embarrassed (about being a virgin) and I wanted to fit in." His army mates took him to Geylang and his sex jaunts continued until he was diagnosed with gonorrhoea recently.

Doctors and social workers interviewed are concerned by the high proportion of teens who went to prostitutes. They believe this is because of the proliferation of online sex sites and forums.

Besides Singapore, some boys also visited prostitutes in neighbouring Johor Baru, Batam and Bangkok, the study found.

Adrian (not his real name), a 21-year-old, has had sex with prostitutes while holidaying in Bangkok. His friends took him to a Geylang brothel and paid for his first sexual encounter when he was 14 or 15.

He has friends who go to Johor Baru regularly to "have fun, as everything from food to prostitutes" is cheaper there.

Adrian, who is waiting to enter polytechnic and says he has stopped visiting prostitutes, added: "The holidays are to chill and to drink, not specifically to have sex. But when it's all boys going on holiday, sex somehow becomes part of the package."