Dec. 10, 2008 — -- Carry -- a Colorado college student who had been in a steady relationship for months -- was recently cajoled by her boyfriend into some sexual experimentation.
He wanted to try anal sex, and even though the 20-year-old said she was "OK with the idea," she nervously downed several drinks before their lovemaking began.
Within 15 seconds, Carry -- not her real name -- said she was "crying and asking him to stop."
They never did it again. But experts say that as social mores ease, more young heterosexuals are engaging in anal sex, a behavior once rarely mentioned in polite circles. And the experimentation, they worry, may be linked to the current increase in sexually transmitted diseases.
Recently, researchers at the Bradley Hasbro Children's Research Center in Rhode Island suggested that anal sex is on the rise among teens and young adults, particularly those who have unprotected vaginal sex.
Experts say girls and young women like Carry are often persuaded to try such sexual behavior for the wrong reasons -- to please a partner, to have sex without the risk of pregnancy or to preserve their virginity. But many don't understand the health consequences.
"It really is shocking how many myths young people have about anal sex," said Judy Kuriansky, a Columbia University professor and author of "Sexuality Education: Past Present and Future."
"They don't think you can get a disease from it because you're not having intercourse," she told ABCNews.com. "They can actually recite by rote how you get AIDS, but it doesn't transfer to their personal behavior."
The study included a comprehensive questionnaire about adolescent sexual and other risk behaviors. The participants self-reported their answers, which scientists say can skew the results in this type of study. To compensate, researchers used audio computer-assisted self -interview technology, allowing participants to enter their responses directly into a computer, rather than having to report to an interviewer.
"Given the subject matter, it is likely that the numbers reported may actually be an underestimate of the prevalence of these behaviors," said Celia Lescano of Brown University, the Bradley Hasbro study's lead author.
More than one-third of new HIV infections in the United States occur among people between the ages of 13 and 29 and can be attributed to the mind-set among youth that they are not at risk of contracting the virus, according to the Kaiser Foundation.