Self-report surveys suggest that half of all 15- to 19-year-olds have had oral sex. That percentage rises to 70% by the time they turn 19, and equal numbers of boys and girls participate. Research indicating that oral sex is less risky to teens' emotional and physical well-being than vaginal sex has been advanced; researchers at the University of California, San Francisco do not believe this conclusion is warranted. They found that oral sex, as well as vaginal sex, was associated with negative consequences. Of adolescents engaging in oral sex only, girls were twice as likely as boys to report feeling bad about themselves and nearly three times as likely to feel used. Despite their behaviors, 90% of adolescents "agree that most young people have sex before they are really ready."