PALO ALTO, CA (ASRN.ORG)- Health Web sites that tell teens about sex are often riddled with errors and omissions, according to new research from Lucile Packard Children's Hospital and the Stanford University School of Medicine. Myths about birth control, sexually transmitted diseases and Pap exams are not dispelled even on several sites reviewed by doctors, the study found.

"Even widely trusted sites like WebMD are not that accurate when it comes to adolescent reproductive health," said lead researcher Sophia Yen, MD, a board-certified specialist in adolescent medicine at Packard Children's and a clinical instructor of pediatrics at Stanford. "Teens should be cautious about finding sexual health answers on the Web." Yen's team identified the top six teen sexual health myths perpetuated by 35 well-trafficked health websites.

The researchers studied Web sites that appeared among the first 10 to 15 hits on Google searches of terms such as "birth control," "morning after pill" and "sexually transmitted disease." The study was the brainchild of Stanford undergraduate and research team member Alisha Tolani, who wondered whether the sex information her friends got from the Web was reliable.

About half of the Web sites, including such highly trafficked destinations as Wikipedia and Mayoclinic.com, failed to provide accurate, complete information about emergency contraception, also known as "the morning-after pill." For instance, sites often failed to say that minors can buy emergency contraception from authorized pharmacists in nine states, and many sites did not correct the myth that emergency contraception causes an abortion. Many Web sites also did not give the World Health Organization's current recommendations for how to use Plan B, the emergency contraception most widely used in the United States. (The guidelines recommend that two of the Plan B pills be taken as soon as after intercourse as possible; the latest point at which the pills may be effective is five days after intercourse.) Sixty percent of the Web sites said the birth control pill causes weight gain, despite recent research showing modern oral contraceptives do not affect body weight. And only 19 percent of the Web sites made it clear that intrauterine devices are safe for adolescents to use.

In addition, only about half of the Web sites surveyed correctly stated that some STDs, such as herpes, can be transmitted through skin-to-skin contact or kissing.

But Yen said the biggest surprise to her in the findings involved Pap exams. Forty percent of Web sites surveyed did not provide accurate information about when young women should receive their first Pap exam. The American College of Obstetrics and Gynecology updated its Pap exam recommendations in 2003 to state that women should receive their first exam three years after initiating sexual activity or at age 21; that is about three years later than the previous recommendations, which Yen's team uncovered on many sites.

Yen worries that the prevalence of outd