More than 200 types of human papillomavirus (HPV) exist, but only a handful cause warts. The specific type determines where warts appear on your body and whether they pose any cancer risk. Common skin warts are caused by HPV types 1, 2, 4, 27, and 57, while genital warts are almost always caused by HPV types 6 and 11. These are all classified as “low-risk” strains, meaning they don’t lead to cancer.
HPV Types Behind Common Skin Warts
The rough, dome-shaped warts that show up on your fingers, hands, and knees are caused primarily by HPV types 2 and 4, with types 1, 3, 7, 27, 29, and 57 also involved. These are the warts most people picture when they hear the word, and they’re the most widespread type of HPV infection overall.
Plantar warts, the painful ones that grow into the soles of your feet, come from a nearly identical group of strains: HPV types 1, 2, 4, 27, and 57. Because they grow inward under the pressure of your body weight rather than outward, they feel like stepping on a pebble, but they’re caused by the same family of viruses as ordinary hand warts.
Filiform warts, the narrow, thread-like growths that tend to appear around the eyelids, lips, and neck, are caused by HPV types 1, 2, 4, 27, and 29. They look different from common warts because of where they grow, but the underlying strains overlap significantly.
Flat Warts and Their Distinct Strains
Flat warts are a separate category with their own set of HPV types: 3, 10, 28, and 49. Unlike common warts, flat warts are smooth, only slightly raised, and tiny, typically 1 to 5 millimeters across (about the size of a pinhead). They tend to be yellowish-brown, pink, or skin-colored, and they almost always appear in clusters, sometimes 100 or more at once. They’re most common on the face, forehead, and backs of the hands, particularly in children and young adults.
HPV Types That Cause Genital Warts
Genital warts are caused by a completely different set of strains than skin warts. HPV types 6 and 11 are responsible for about 90% of all genital wart cases. These strains spread through sexual contact, including vaginal, anal, and oral sex, as well as intimate skin-to-skin contact. The incubation period ranges from 3 weeks to 8 months, so warts can appear long after the initial exposure.
Risk factors for genital warts include younger age at first sexual activity, multiple sexual partners, inconsistent use of barrier protection, smoking, and a weakened immune system.
Low-Risk vs. High-Risk HPV
All of the HPV types that cause visible warts, whether on your hands, feet, or genitals, are classified as low-risk. This means they don’t cause cancer. The strains behind common skin warts (types 1 through 4 and their relatives) carry zero cancer risk. HPV 6 and 11, the genital wart strains, are also non-cancerous.
High-risk HPV types are a separate group entirely. Types 16 and 18 are the most dangerous, responsible for roughly 66% of cervical cancers and most other HPV-related cancers. These high-risk strains typically don’t produce visible warts at all, which is why screening matters even when no symptoms are present. Having genital warts doesn’t mean you have a cancer-causing strain, though it’s possible to be infected with both low-risk and high-risk types at the same time.
How HPV Creates a Wart
HPV enters through tiny breaks in the skin, even microscopic ones you can’t see. The virus targets the deepest layer of skin cells and essentially hijacks their growth controls. Normally, skin cells stop dividing as they mature and move toward the surface. HPV produces proteins that override this process, forcing mature cells to keep multiplying. At the same time, the virus blocks the cell’s built-in self-destruct mechanism, which would ordinarily kill off cells behaving abnormally. The result is a dense mound of excess skin cells: a wart.
This is why warts tend to appear in areas prone to cuts, friction, or moisture. Nail biters frequently get warts around their fingertips. Plantar warts are more common in people who walk barefoot in wet communal areas like pool decks and locker rooms, where the virus thrives and skin is softened enough for entry.
Vaccine Protection Against Wart-Causing Strains
The current HPV vaccine (Gardasil 9) protects against nine HPV types, including types 6 and 11, the strains behind most genital warts. In clinical trials, the vaccine showed 99% efficacy at preventing genital warts. It also covers seven high-risk cancer-causing types, including 16 and 18.
The CDC recommends vaccination starting at age 9 to 12, with catch-up vaccination available through age 26. Adults between 27 and 45 who weren’t previously vaccinated can also receive the vaccine on a three-dose schedule. The vaccine does not protect against the HPV types that cause common skin warts on the hands and feet, since those strains (types 1, 2, 4, and others) aren’t included in the formulation. Skin warts are considered a nuisance rather than a health threat, which is why vaccine development has focused on genital and cancer-causing strains.