The number of teenage boys who have visited prostitutes is on the rise, a trend that has researchers worried as some do not use condoms consistently, may catch sexually transmitted diseases and go on to infect their girlfriends. In the first-ever study of Singapore youth who have had sex with prostitutes, it was found that about two in five of the teens surveyed had paid for sex. The interviews were conducted with some 300 heterosexual boys aged between 16 and 19 who went to a government specialist clinic that treats sexually transmitted infections (STIs), between 2009 and 2014.