Sexually transmitted infections

Each year, between 8 and 10 million American teens contract a sexually transmitted disease. According to the U.S. Centers for Disease Control, almost half of the 19 million sexually transmitted diseases reported in the U.S. occur in young people, ages 15 to 24. Lloyd Kolbe, director of the CDC's Adolescent and School Health program, called the STI problem "a serious epidemic." The younger an adolescent is when they first have intercourse, the more likely they are to get a STI throughout their teenage years.

Human papillomavirus (HPV) is the most common STI among teens as well as adults. In the CDC study, 18% of teen girls were infected with HPV. Another study found that HPV infections account for about half of STIs detected among 15- to 24-year-olds each year. While most HPV infections cause no disease, HPV does cause genital warts and cervical cancer. An HPV vaccine protects women against two HPV types which cause 70% of cervical cancers as well as two types associated with 90% of genital warts. Ideally the woman should be vaccinated before initial sexual activity, since the vaccine is only effective before exposure to the HPV types.

A 2008 study by the CDC found that one in four teen girls, or an estimated 3 million girls, has an STI. The study of 838 girls who participated in a 2003–04 government health survey found the highest overall prevalence among black girls, nearly half in the study were infected, compared with 20 percent among both whites and Mexican-American teens. The same study found that, among those who were infected, 15% had more than one STI, and 20% of those who said they had only one sexual partner were infected.

In the CDC study, 4% were infected with chlamydia, historically the most prevalent of all STIs in the general population. More than a third of all chlamydia cases occur in those aged 15 to 19.

In the CDC study, 2% were infected with herpes simplex. The herpes infection rate fell between 1988 and 2004 among teens as well as the overall population. Overall, the number of Americans aged 14 to 49 who tested positive for herpes 2 infection fell by a relative rate of 19 percent between 1988 and 2004—from 21 percent in the late 1980s and early 1990s to 17 percent 10 years later, the researchers reported. The number of people aged 14 to 19 who tested positive for new herpes simplex 2 infections dropped from 5.8 percent in a 1988–1994 survey to just 1.6 percent 10 years later.