More than 200 types of human papillomavirus (HPV) have been identified, making it one of the most genetically diverse virus families that infects humans. These types are sorted into five major groups based on their genetic makeup, and they range from completely harmless skin infections to strains that can cause cancer. The number that matters most for your health is much smaller: about 14 types are classified as high-risk, and just two of those are responsible for the majority of HPV-related cancers.
How HPV Types Are Classified
Scientists group the 200-plus HPV types into five broad categories called genera: Alpha, Beta, Gamma, Mu, and Nu. Types within different groups share less than 60% of their genetic code in the key gene used for comparison. In practical terms, these groups reflect where the virus prefers to live in your body. Alpha types mostly infect mucosal surfaces like the genitals, mouth, and throat. Beta and Gamma types, along with Mu and Nu, primarily infect regular skin on your hands, feet, and elsewhere.
Most people will only ever hear about a handful of these types, because only a fraction cause noticeable symptoms or pose a serious health risk. The rest quietly infect skin cells, trigger an immune response, and clear on their own without you ever knowing.
The 14 High-Risk Types
Fourteen HPV types are considered high-risk, or oncogenic, meaning they can lead to cancer. These are types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, and 68. They work by interfering with the normal controls that prevent cells from growing out of control. Over years or decades, persistent infection with one of these types can cause cells to turn precancerous and eventually malignant.
Not all high-risk types carry equal weight. HPV 16 alone causes roughly half of all cervical cancers worldwide. Combined with HPV 18, those two types account for about 76% of cervical cancer cases, according to the World Health Organization. The same two types are the primary drivers of HPV-related cancers of the throat, anus, penis, vulva, and vagina. This is why screening tests and vaccines focus so heavily on types 16 and 18 specifically.
Low-Risk Types and Genital Warts
Low-risk HPV types don’t cause cancer, but they can cause visible warts. The two most important are types 6 and 11, which are responsible for about 90% of genital warts. These warts can appear on or around the genitals, anus, mouth, or throat. They’re not dangerous, but they can be uncomfortable and stressful to deal with.
In rare cases, types 6 and 11 cause a condition called recurrent respiratory papillomatosis, where warts grow in the airway, typically the larynx. This can happen in infants and young children, possibly transmitted during birth from a mother with genital warts. The risk is low, but the condition can cause breathing difficulties and often requires repeated treatment.
Types That Cause Skin Warts
A separate set of HPV types causes the common warts most people have encountered on their hands or feet. These are distinct from the sexually transmitted types and spread through ordinary skin contact or contaminated surfaces.
- Common warts on the hands are most often caused by HPV types 2 and 4, with types 1, 3, 7, 27, 29, and 57 also contributing. They feel rough and bumpy and sometimes have tiny black dots (clotted capillaries, not seeds).
- Flat warts are smaller, smoother, and tend to appear in clusters of 20 to 100. They’re caused by types 3, 10, and 28.
- Filiform warts look like thin threads and typically grow on the face near the mouth, eyes, or nose. Types 1, 2, 4, 27, and 29 are responsible.
- Plantar warts grow on the soles of the feet and are commonly caused by HPV type 1.
These skin warts are generally harmless and often resolve on their own, though they can take months or years to clear. They have no connection to cancer risk.
What HPV Tests Actually Look For
When you get an HPV test during cervical screening, the test doesn’t check for all 200-plus types. Standard FDA-approved tests screen for the 14 high-risk types only. The most widely used test identifies HPV 16 and HPV 18 individually, since those two carry the highest cancer risk, while pooling the remaining 12 high-risk types into a single result. If the pooled result is positive, your doctor knows a high-risk type is present but may not know exactly which one.
This design reflects the clinical reality: knowing whether you carry type 16 or 18 changes how aggressively your doctor monitors you, while the other high-risk types warrant attention but carry somewhat lower individual risk. There is no routine clinical test for low-risk types or the many skin-only types, because there’s no medical reason to screen for them.
What the Vaccine Covers
The current HPV vaccine used in the United States, Gardasil 9, protects against nine of the 200-plus types. It targets the seven high-risk types responsible for the largest share of cancers (16, 18, 31, 33, 45, 52, and 58) plus the two low-risk types that cause most genital warts (6 and 11). Those seven high-risk types collectively cause the vast majority of HPV-related 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 doesn’t treat existing infections, but in people who haven’t yet encountered these specific types, it’s highly effective at preventing the infections that lead to cancer and warts. The remaining HPV types not covered by the vaccine are either very rare causes of cancer or cause only minor skin conditions.