A study of sexually-active American teenagers says that almost one in ten has same-sex partners.

The research, carried out by the New York City health department, found that 9.3 per cent of the sexually active teenagers said they were intimate with partners of the same sex.

In 2002, a similar study of teenagers in Vermont and Massachusetts found that only five to six per cent had same-sex partners.

However, the latest study found that teenagers who only sleep with partners of the same sex, or sleep with both sexes, are at a higher risk of sexually-transmitted infections because they are less likely to use condoms.

The study of 17,000 young people in New York City also found that teenagers who displayed bisexual behaviour were far more likely to have been forced into sex. Around a third of these teenagers said they had been forced into sex, compared to just six per cent of heterosexual boys and 16 per cent of straight girls.

Meanwhile, more than half of boys who had sex with both genders did not use a condom, compared to heterosexual teenagers.

Elizabeth Saewyc, a researcher at the University of British Columbia, told Reuters Health that gay and bisexual teenagers may engage in riskier sexual behaviour because sex education is not relevant to them.

“Some teens I’ve seen tell me that they completely check out of sex ed because they feel what they were learning didn’t apply to them,” she said.

The research was published in the journal Paediatrics.