A new study analyzing the sex practices of people ages 16-22 finds that heterosexual teens and young adults are increasingly open to sexual experimentation, with significant increases in often-painful anal and oral sex experiences compared to adolescents in 1990.

The study, "Heterosexual Practices Among Young People in Britain: Evidence From Three National Surveys of Sexual Attitudes and Lifestyles," was published in the Journal of Adolescent Health in December. Researchers conducted more than 45,000 interviews of young adults between 2010 and 2012 and found that one-in-four men and one-in-five women report having vaginal, oral and anal sex over the past year. Previous surveys conducted between 1990 and 1991 found that only 1-in-10 young adults had performed all three vaginal, oral and anal sex in the past year.

The study shows a particular increase in vaginal sex engaged in by 16-to 24-year-olds, but the increasing oral and anal sex practices was more most significant among slightly older participants between 19 and 24. Despite a small overall drop in vaginal intercourse among both age groups, the researchers write that oral and anal sex are not "replacing" vaginal sex. The median age of one's very first heterosexual experience of any kind, such as kissing, was 14. The median age for first intercourse (oral, vaginal or anal) among men and women born between 1990 and 1996 was 16 years old.

"[W]e are seeing oral and anal sex joining, rather than replacing, vaginal intercourse in heterosexual repertoires," write the study authors. "Moreover, despite the increasing prevalence of anal intercourse, the low prevalence of reporting recent experience may indicate it is a less regular feature in young people's sexual interactions."

The researchers addressed the gender gap regarding the personal preferences of heterosexual anal sex partners, noting a strong social trend of normalizing often "painful" sexual practices, such as anal intercourse.

Interviews shwoed "repeated engagement in disliked sexual activities (mainly oral-penis contact and anal intercourse) was four times more common among women than men." They also noted, "prominent cultural discourses among teenagers that normalize painful, and sometimes coercive, anal intercourse with men tending to talk more positively about the practice than women."

The researchers acknowledged that despite the large sample size of interviews, same-sex interactions and a "complex socio-sexual landscape" can always skew self-reported sexual habit data. In particular, the increase in anal and oral sex practices should be considered by health officials educating young people.

"Recent decades have seen an earlier age at initiation of partnered sexual experiences and increased diversity in heterosexual practices among young people," write the study co-authors. "Keeping pace with trends in sexual practices is necessary to safeguard young people's health and to support them in increasing their sexual well-being."

The study authors also caution that recent studies and high-profile stories analyzing pornography's effect on young people's sexual habits are still equivocal. Bryant Paul, an associate professor at Indiana University's Media School and author of research on adolescent porn habits, said boys are 13 and girls are 14 when they first view pornography.

Study lead author Dr. Ruth Lewis, who conducted the research at the London School of Hygiene & Tropical Medicine, said "keeping pace" with current trends in sexual practices is often a difficult task.

"By shedding light on when some young people are having sex and what kinds of sex they are having, our study highlights the need for accurate sex and relationships education that provides opportunities to discuss consent and safety in relation to a range of sexual practices," Ruth writes in a release. "This will equip young people with the information and skills they need to maximise their wellbeing from the outset of their sexual lives."

Researchers at Indiana University’s Kinsey Institute for Research in Sex, Gender, and Reproduction conducted surveys of sexual behaviors earlier this year, revealing that one-third of women say they've had anal sex and.   Forty-three percent of heterosexual male respondents said they'd had anal sex at least once in their lifetime, while 37 percent of women said they'd been on the receiving end of anal sex at least once.