Oral sex is often a precursor to teenagers having intercourse, concludes a new study published in Archives of Pediatric and Adolescent Medicine. The study asked more than 600 high school students in California to report on their sexual experiences by filling out surveys twice a year, from the beginning of ninth grade, in 2002, to the end of 11th grade, in 2005.

From the questions asked on the survey, and the six-month window in between each one, researchers learned that most adolescents have their first experiences with oral sex and vaginal intercourse in the same six-month period. They could not extrapolate which experience came first but discovered that among teens who initiated only one of the two types of sex during that six-month window, oral sex usually preceded vaginal intercourse. Additionally, having oral sex once made intercourse more likely to occur. Specifically, initiating oral sex by the end of their freshman year in high school gave teens a 25 percent chance of initiating vaginal sex around the same time and a 50 percent chance of initiating intercourse by the end of their junior year. The results of the study did not vary across any racial, ethnic or gender boundaries.

The goal of the study was to establish the relationship between oral and vaginal sex and whether teens used oral sex as a means of delaying intercourse or if oral sex increased the likelihood of having vaginal sex. The study found the latter to be true, partly because most adolescents don't consider oral sex to be sex in the first place.

"We don't talk about the risks that are inherent in oral sex," says Bonnie Halpern-Felsher, Ph.D, senior author of the study and a professor of pediatrics at the University of California San Francisco. "Teens think oral sex is less risky [than intercourse] and they're right, it's not risk free but it is less risky. But socially and emotionally, they're still being intimate."

Halpern-Felsher believes teenagers are most likely to initiate oral and vaginal sex during their first two years of high school. She advises concerned parents to talk to their teens about oral sex and not focus solely on the risks associated with intercourse.

"We have a disadvantage as health professionals and parents when teens do not equate oral sex with sex," says Halpern-Felher. "They think the messages don't apply to them and we need to make it apply to them, we need to talk to them about oral sex."