Twelve types of HPV are classified as high-risk for cancer: HPV 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, and 59. Of these, HPV 16 and HPV 18 are by far the most dangerous, responsible for the majority of HPV-related cancers across multiple body sites. But having a high-risk HPV infection doesn’t mean cancer is inevitable. Most infections clear on their own, and only a small fraction persist long enough to cause cellular changes that can eventually become cancerous.
HPV 16 and 18: The Two Highest-Risk Types
HPV 16 and HPV 18 together cause about 70% of cervical cancers worldwide. HPV 16 is also the dominant type found in throat cancers, anal cancers, and most other HPV-related cancers. These two types are singled out because their viral proteins are especially effective at disabling the body’s built-in cancer defenses.
Here’s what happens at the cellular level: high-risk HPV produces two proteins that interfere with tumor suppression. One protein latches onto p53, a molecule your cells rely on to detect and repair DNA damage, and marks it for destruction. The other targets a second protective molecule called pRb, which normally keeps cell division in check. With both of these safeguards knocked out, infected cells can accumulate genetic damage and divide uncontrollably. This process typically takes years or even decades, which is why HPV-related cancers usually appear in middle age rather than shortly after infection.
The Full List of High-Risk Types
Beyond HPV 16 and 18, ten other types carry cancer risk: HPV 31, 33, 35, 39, 45, 51, 52, 56, 58, and 59. These are all classified as carcinogenic by the International Agency for Research on Cancer. Individually, each of these types causes a much smaller share of cancers than 16 or 18, but collectively they account for a meaningful portion, particularly in cervical cancer.
Low-Risk Types Are Different
Not all HPV types pose a cancer threat. There are over 200 known HPV types, and most are either harmless or cause minor issues like common skin warts. The low-risk types people hear about most often are HPV 6 and HPV 11, which cause roughly 90% of genital warts. These types don’t produce the same tumor-suppressing protein disruption that high-risk types do, so genital warts themselves are not precancerous and don’t develop into cancer.
Which Cancers HPV Causes
HPV’s role in cancer extends well beyond the cervix. Here’s how much each cancer type is driven by HPV:
- Cervical cancer: Over 90% of cases are caused by HPV
- Anal cancer: Over 90% of cases
- Oropharyngeal (throat) cancer: About 60% to 70% of cases, specifically cancers at the base of the tongue, tonsils, and back of the throat
- Vulvar cancer: About 69% of cases
- Vaginal cancer: About 70% of cases
- Penile cancer: About 63% of cases
Oropharyngeal cancer linked to HPV has been rising sharply in recent decades, particularly among men. While throat cancers were once associated primarily with tobacco and alcohol, HPV (especially type 16) is now the leading cause in many countries.
Most HPV Infections Never Become Cancer
An HPV infection, even with a high-risk type, usually resolves without treatment. The immune system clears most infections within months. In one study tracking men over time, about 75% tested negative for HPV within 12 months of initial detection, with a median clearance time of roughly six months. The timeline is similar for oncogenic and non-oncogenic types alike.
Cancer develops only when a high-risk infection persists for years. A small percentage of infections escape immune clearance and become what’s called a persistent infection, where the virus integrates into the host cell’s DNA and continuously produces those tumor-disrupting proteins. Factors that increase the risk of persistence include a weakened immune system, smoking, and co-infection with multiple HPV types. Even among persistent infections, the progression from initial cellular changes to invasive cancer typically takes 10 to 20 years, which creates a long window for detection through screening.
How Screening Catches High-Risk HPV
Cervical cancer screening has shifted toward directly testing for high-risk HPV DNA rather than relying solely on Pap smears, which look for abnormal cells under a microscope. An HPV DNA test identifies whether high-risk viral genetic material is present in cervical cells. A large study involving over one million women found that a negative HPV test provides stronger reassurance against future cervical cancer risk than a negative Pap test alone.
Current guidelines from the World Health Organization recommend that 70% of women be screened with a high-performance HPV test by ages 35 and 45. In the United States, screening options include HPV testing alone or HPV testing combined with a Pap smear. There is no approved HPV screening test for the other cancer sites (throat, anal, penile, vulvar), though research into screening for some of these is ongoing.
What the HPV Vaccine Covers
The current vaccine used in the United States, Gardasil 9, targets nine HPV types: 6, 11, 16, 18, 31, 33, 45, 52, and 58. Types 6 and 11 are included to prevent genital warts, while the other seven are the high-risk types responsible for the largest share of HPV-related cancers. This combination gives the vaccine the potential to prevent more than 90% of HPV-caused cancers.
The vaccine works best when given before any exposure to the virus, which is why it’s recommended starting at age 11 or 12. It’s approved for people up to age 45 in the U.S., though the benefit decreases with age since most adults have already encountered at least some HPV types through sexual contact. The vaccine does not treat existing infections or clear HPV that’s already present, so it complements screening rather than replacing it.