HPV infects the epithelial cells, which cover the inner and outer surfaces of the body including the skin, throat, genital tract, and anus. Once the epithelial cells are infected, the virus initiates the production of proteins that can interfere with normal cell function, enabling the cells to grow uncontrollably. As the persistently infected cells continue to grow, they may develop mutations that promote even more cell growth. This leads to the formation of a high-grade lesion and, ultimately a tumor. Research studies have shown that it can take 10-20 years from the time of an initial HPV infection until a tumor is produced. In fact, even high-grade lesions do not always lead to cancer. The percentage of high-grade cervical lesions that progress to invasive cervical cancer has been estimated to be 50% or less.
Sexually transmitted HPVs fall into two categories:
Low-risk HPVs usually do not cause cancer but can cause skin warts on or around the genitals or anus. HPV types 6 and 11 cause 90% of all genital warts.
High-risk HPVs, also know as oncogenic HPVs, can cause cancer. Types 16 and 18 are responsible for the majority of HPV-caused cancers.
Since the virus infects skin cells, HPV infections can be easily spread through direct skin-to-skin contact during vaginal, anal and oral sex. Condom use reduces the risk of transmitting HPV but does not completely prevent transmission.
High-risk HPVs cause virtually all cervical cancers. While many HPV infections resolve within 1-2 years, infections that last for many years may increase a person's risk of developing cancer.
Symptoms of HPV viral infection are rare; the majority of individuals infected are unaware that they have contracted HPV. Most infections spontaneously resolve within a few months without the formation of lesions. Progression to invasive cancer can be prevented when subclinical HPV infection is detected early and regular examinations are performed.