Human papillomavirus (HPV) comes in more flavors and colors than Baskin & Robbins. Many of its 70-plus strains may be all too familiar, such as the ones that cause warts from top (mouth) to bottom (feet) and, alas, in between (yes, genitals). But 13 other strains, which cause anal and cervical cancer, are truly the ones to watch out for.

Prevention of this extremely common infection is very difficult. Unlike HIV, HPV can be transmitted through touch, though condom use can help limit its penetration. Treatment varies from sorbet smooth (laser removal of a few slightly abnormal cervical cells) to rocky road (extensive surgery on precancerous cells in the anus can keep you rocked by pain for weeks). For women, cervical Pap smears are universally promoted for the screening of abnormal cells, a standard of care that has caused cervical cancer rates to dive. As for anal cancer -- particularly common among gay men, but not unheard of among women and straight men -- the medical community has been slow to catch on, making decisions on screening and treatment a tough nut to crack. For the state of the art on these two dangerous cancers, read on.