Human papillomavirus, or HPV, is a group of viruses that infects more than 6.2 million American men and women each year. About 40 of the more than 100 varieties are transmitted through sexual contact. There is no cure for HPV, but most infections clear without treatment in mere months. There are, however, several high-risk strains that can linger, causing precancerous lesions or full-blown cancer. These require immediate medical attention to control. The 40 strains of HPV that affect the genitals are passed through sexual contact. Symptoms do not need to be present to pass the virus to another person. HPV can be passed to and from the skin of the penis, vulva, or anus, as well as the linings of the vagina, cervix, and rectum. In rare cases, genital HPV can also be passed from mother to child during a vaginal birth. Since most strains have adapted to specific areas of the body, not all contact is a potential way to spread HPV. Hand-to-genital contact, for example, is unlikely to infect the hand.