If you were a teen girl within the last two decades, there's no doubt you were warned about the dangers of the human papillomavirus (HPV) and told to get the HPV vaccine . That's because the STI actually changes the cells of your cervix, which can lead to cervical cancer down the line if it goes unchecked, Dr. Shirazian says. Plus, the virus is very common (over 70% of people in the U.S. have it), which is why it's a good idea for pretty much everyone to get the vaccine — regardless of gender — before they become sexually active.However, "there are over a hundred subtypes of HPV, and the classic vaccine, Gardasil, only covers four of them," Dr. Shirazian explains. Granted, these are the strains most likely to cause aggressive cancer and the ones you're most likely to come across in the U.S. But it's possible to become infected with a different strain, especially if you're out of the country.That doesn't mean you should skip out on the vaccine, though. "It still protects you against the most aggressive strains and those that lead to cancer most frequently," Dr. Shirazian says. "To me, that feels pretty great."