The National Center for Health Statistics, a division of the Centers for Disease Control and Prevention, released data today that revealed an overall decrease in oral sex among adolescents between 2002 and 2010, reflecting a similar small decline in vaginal intercourse within the same age group.
A drop in oral sex was seen among females, but the numbers of males engaged in the behavior was the same.
Experts said two-thirds of all youth between the ages of 15 and 24 had had an experience with oral sex, risky behavior that the federal government said is contributing to the spread of sexually transmitted diseases.
The report, "Prevalence and Timing of Oral Sex With Opposite-Sex Partners Among Females and Males Aged 15-24 Years: United States," included data from the CDC's National Survey of Family Growth. The data came from 6,346 interviews among young adults from 2007 to 2010
In the youngest group, ages 15 to 19, which did not include married males, the report said that 41 percent of females and 47 percent of males had received oral sex. Forty-three percent of girls in that group had given oral sex, while 35 percent of boys had.
For both sexes between the ages of 20 to 24, the numbers go up: 81 percent of females and 80 percent of males had engaged in oral sex.
Some data suggest that many adolescents engage in oral sex because they believe it is safer and preserves their virginity, according to a CDC 2009 fact sheet.
"In our culture, there was a time when the president suggested that oral sex wasn't sex, and that is still with us, to some degree," said Geoffrey Michaelson, a Vienna, Va., psychologist who specializes in sexuality.
"Intercourse, frankly, is considered more intimate, the last step in the baseball analogy," said Michaelson. "There is a whole mystique about what is OK and what is not OK, but it's all self-delusion.
"From my point of view, any exchange of body fluid, touching, fondling or arousal, that is sex," he said.
The CDC has taken an increased interest in the data because of the rise of sexually transmitted diseases, including a spike in HIV infection rates among males 13 to 29 years old.
Although the risk for HIV/AIDS through oral sex is lower than vaginal intercourse or anal sex, according to the CDC, the transmission rates for genital herpes, gonorrhea and syphilis are considerably higher.
Some studies have found that an increase in oral cancers in the United States is associated with the human papillomavirus, and researchers attribute that to the popularity of oral sex.
One of the findings of the NCHS report was that of those adolescents who'd had oral sex, only 5.1 percent of females and 6.5 percent of males stopped there. The overwhelming majority of 15- to 24-year-olds went on to have vaginal intercourse.
These findings underscore previous studies that found having oral sex was a strong indicator for engaging in sexual intercourse.
A 2010 study in the Archives of Pediatric Adolescent Medicine suggested that teens who engaged in oral sex were likely to go on to vaginal sex shortly after their first oral sex activity.
Researchers at the University of California at San Francisco and UC Merced found that half the teens who engaged in oral sex in the ninth grade were likely to begin having intercourse by the 11th grade. The most sexually active ones will have intercourse within six months.
Deborah Tolman, a professor of psychology at Hunter College in New York City and former director of the Center for Research on Gender and Sexuality at San Francisco State University, said that latest statistics did not surprise her.
But Tolman said the numbers were not as important as "what it means. ... Why are they making those choices and what kind of an experience is it?"
Tolman said that cultural attitudes about risky behaviors needed to be understood for prevention programs to work.
Non-Hispanic white females reported having oral sex more often (69 percent) than non-Hispanic black females (63 percent) or Hispanic females (59 percent).
"The differential in race and ethnicity is not biological," she said. "It's about meaning. Why do people choose different behaviors in different cultures?"
She also worried about the gender imbalance between "who gives and who gets" oral sex.
"In order to support safe decisions, we have to recognize the meaning of these behaviors and how heterosexual relationships are negotiated," said Tolman.
"Our girls need to know they are entitled to make a choice," she said. "They are engaging in behaviors out of various forms of pressure -- relationship and emotional pressure."
Psychologist Michaelson said the new report underscored the importance of sex education.
"What we are up against is everything these kids see in the movies and what their parents' comfort and discomfort is when they talk to them," he said. "In all the advertising, we say, 'Talk to your kids about drugs.' Where are the ads that say, 'Talk to your kids about sex'?"
Overall for adolescents, less than one-third -- 29 percent of females and 28 percent of males -- had had no sexual experience at all with the opposite sex, according to the report.
But those numbers might be misleading, according to Michaelson, who said adolescents are notorious for not speaking honestly about sex.
"There is also mythology and truth in high schools," he said. "Is everyone doing it? ... Some of my friends lied to me."