Dr. Donald Brown inoculated Kelly Kent with the HPV vaccine in his Chicago office in the summer of 2006 — not long after the first version of the vaccine reached the market. Charles Rex Arbogast/AP hide caption

itoggle caption Charles Rex Arbogast/AP

Kids as young as 13 purchase e-cigarettes, or "vape pens," online, where independent sellers don't necessarily ask a buyer's age. Jenny Lei Bolario/Youth Radio hide caption

itoggle caption Jenny Lei Bolario/Youth Radio

Solid friendships can help buffer life's stress. iStockphoto hide caption

itoggle caption iStockphoto

Condom use has dropped among black youth, even as teens engage in less risky sexual behavior overall. Mike Segar/Reuters/Landov hide caption

itoggle caption Mike Segar/Reuters/Landov