Two-thirds of teens and young adults have had oral sex - about as many as have had vaginal intercourse, suggests research by the Centers for Disease Control and Prevention.
The data speak to changing social mores and the need to educate teens about the risk of contracting a sexually transmitted disease from oral sex, experts say.
The study is part of the government's effort to monitor those at risk for sexually transmitted diseases even though they aren't yet at risk for pregnancy if they're only having oral sex, says Casey Copen, a demographer with the CDC's National Center for Health Statistics.
The research shows that one in four teens is now having oral sex before vaginal sex - marking the "hierarchical reordering of oral sex in American culture," says Justin Garcia, an evolutionary biologist with the Kinsey Institute at Indiana University.
Many sex researchers had believed that oral sex was being used to defer vaginal sex, but that doesn't seem to be the case for most teens today, says Terri Fisher, a professor of psychology at Ohio State University.
The only demographic group that postponed vaginal sex until substantially after oral sex were young white girls of educated mothers - perhaps those whose mothers impressed upon them the need to avoid teenage pregnancy, researchers say.
Fisher says she also was struck by the fact that girls and boys gave and received oral sex equally and that sexual activity began at roughly the same age, with 44% of 15- to 17-year-old boys and 39% of girls of that age engaging in some kind of sexual activity with an opposite-sex partner.
"It certainly would suggest that the gender differences found previously no longer exist," Fisher says.
The CDC study is based on 6,346 interviews from 2007 to 2010, conducted anonymously via computer. Those interviewed ranged in age from 15 to 24.
The study also found some racial differences: Non-Hispanic blacks generally began vaginal sex earlier than whites, and whites were more likely to engage in oral sex before vaginal intercourse.
Other research suggests that more young people are deferring all types of sexual activity later than their parents and grandparents did.
A need for more education?
The new figures suggest that sex education programs need to directly address oral sex as well as vaginal intercourse, says Craig Roberts, an epidemiologist at the University of Wisconsin-Madison's University Health Services department and a member of the American College Health Association.
There's no such thing as totally "safe sex," Roberts says, though oral sex reduces pregnancy risk to zero and HIV risk to almost nothing. But he notes that people who perform or receive oral sex are still at risk for other sexually transmitted diseases such as herpes, gonorrhea and chlamydia.
Condom use is unlikely during oral sex, he and others add.
The growing frequency of oral sex means parents also need to address it with their children, says Heather Eastman-Mueller, a sexuality educator at the University of Missouri.
Instead of worrying about "the" talk, though, she advises parents to consistently talk in age-appropriate ways about sexuality, morality and physical self-esteem.
"It should be a conversation you have all the time," Eastman-Mueller says.