Of the over 100 types of human papillomavirus (HPV), more than 40 can be sexually transmitted. Genital HPV infection is very common, with a point prevalence among women worldwide of approximately 10 percent. In most cases, HPV infection is either cleared or becomes undetectable and causes no disease; however, persistent HPV infection is causally related to all cervical cancers and genital warts. In addition, a large proportion of other cancers, such as vaginal, vulvar, anal, and penile cancers as well as many cancers of the head and neck, are associated with HPV infection. Moreover, recurrent respiratory papillomatosis (RRP) is a potentially serious disease caused by HPV types typically responsible for genital warts. RRP can lead to severe airways obstructions and may require repeated surgical interventions. HPV types are typically divided into high-risk types, most often associated with cancers, and low-risk types, typically associated with warts. High-risk types 16 and 18 are responsible for approximately 70 percent of cervical cancers worldwide, whereas low-risk types 6 and 11 are responsible for approximately 90 percent of genital warts.