Gardasil is a vaccine recommend to pre teens to protect from HPV.

HPV is an STI that most people get in their lifetime (the vaccine is rather recent). While the body can normally fight it off, in the cases that it doesn't, it can cause cancer in both men and women. Almost all cervical cancer is caused by HPV.

In men, HPV is normally asymptomatic and there is no way to test for it. Men are actually much more likely (four times as likely) to get HPV than women. But, while it can cause cancer in both sexes, men have a far lesser chance of developing HPV related cancer than women.

Because of this, it's seen largely as just a women's problem and many doctors only recommend the shot to girls, not boys. I find this absolutely ridiculous. Because of this, men pass it on to women without knowing, and are at risk themselves.