More than 200 types of human papillomavirus (HPV) have been identified, but only a few dozen regularly infect people in ways that cause noticeable problems. The types that matter most fall into two broad categories: low-risk types that can cause warts but not cancer, and high-risk types that can trigger several kinds of cancer if the infection persists for years.
High-Risk HPV Types
Twelve HPV types are classified as high risk: 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, and 59. These strains don’t cause visible warts. Instead, they quietly infect cells in the cervix, throat, anus, or genital skin and can, over time, cause those cells to turn cancerous. High-risk HPV is detected in 99% of cervical precancers.
Not all high-risk types carry equal weight. HPV 16 alone causes roughly half of all cervical cancers worldwide. Together, HPV 16 and 18 account for about 70% of cervical cancers. Five additional types (31, 33, 45, 52, and 58) are responsible for another 15% of cervical cancers and 11% of all HPV-associated cancers combined.
Beyond the cervix, high-risk HPV can cause six types of cancer overall: cervical, anal, oropharyngeal (back of the throat, base of the tongue, and tonsils), penile, vaginal, and vulvar. Oropharyngeal cancer linked to HPV has been rising sharply in recent decades, particularly in men.
Low-Risk HPV Types
Low-risk HPV types don’t lead to cancer, but they can cause genital warts. HPV 6 and HPV 11 are responsible for about 90% of genital wart cases. These warts appear as small, flesh-colored bumps or clusters on or around the genitals or anus. They’re often painless, though they can itch or cause discomfort. While genital warts are treatable and not dangerous, they tend to recur, and many people find them distressing.
Cutaneous Types That Cause Skin Warts
A separate group of HPV types infects only the outer layers of skin, not the mucous membranes of the genitals or throat. These cutaneous types cause the common warts most people recognize from childhood.
- Common warts (rough, raised bumps usually on hands and fingers) are most often caused by HPV types 2 and 4, with types 1, 3, 27, 29, and 57 also involved.
- Plantar warts (deep, painful warts on the soles of the feet) are primarily caused by HPV type 1, though several of the same types behind common warts can also be responsible.
These skin wart types spread through direct contact or shared surfaces like locker room floors, not through sexual contact. They’re a nuisance rather than a health threat, and most resolve on their own within a year or two, especially in children.
How Most Infections Resolve on Their Own
The vast majority of HPV infections, whether high risk or low risk, clear without treatment. In a prospective study tracking women over time, about 81% had cleared their HPV infection within a median of 19 months. Your immune system gradually eliminates the virus, and in most cases you’d never know you had it.
The concern is the small percentage of infections that persist. When a high-risk type lingers for years, it can slowly cause cell changes that progress toward cancer. This is why cervical screening exists: it catches those cell changes early, long before cancer develops. The process from initial infection to cancer typically takes 10 to 20 years, which provides a wide window for detection.
How Screening Works
Modern cervical screening uses an HPV DNA test that checks for the presence of high-risk types. The test specifically identifies whether HPV 16 or 18 is present, since those two carry the highest cancer risk. If either one is found, your doctor will typically recommend a closer look right away, such as a colposcopy. The test also detects the remaining 12 high-risk types as a group, and a positive result for those may lead to additional monitoring or a Pap test to check for abnormal cells.
There is no approved screening test for HPV in men, and no routine test for the low-risk types that cause warts. Genital warts are diagnosed visually.
What the Vaccine Covers
The HPV vaccine used in the United States (Gardasil 9) protects against nine specific types: 6, 11, 16, 18, 31, 33, 45, 52, and 58. That covers the two low-risk types behind most genital warts and seven of the high-risk types responsible for the large majority of HPV-related cancers. Vaccination is recommended starting at age 11 or 12 and is approved for people through age 45, though it’s most effective when given before any exposure to the virus.
Because the vaccine doesn’t cover all high-risk types, routine cervical screening remains important even for vaccinated individuals. Still, the nine types included in the vaccine account for roughly 90% of cervical cancers and 90% of genital wart cases, making it one of the most effective cancer prevention tools available.