Warts are caused by the human papillomavirus, commonly known as HPV. The virus infects the top layer of skin, usually through a small cut or scrape, and triggers the skin cells to grow rapidly into the tough, raised bumps you recognize as warts. There are over 100 types of HPV, but only a handful are responsible for the skin warts that show up on your hands, feet, and face.
How HPV Creates a Wart
HPV targets keratinocytes, the cells that make up the outermost layer of your skin. Once the virus gets inside these cells, it hijacks their normal growth cycle. Specifically, it interferes with the signals that tell skin cells when to stop dividing and start maturing. The virus also pushes skin stem cells to multiply faster than they normally would, which is why warts develop that characteristic thick, rough texture. The result is a small mound of excess skin that the virus uses as a home base to keep replicating.
This process isn’t instant. After initial exposure, warts can take weeks to many months before they become visible. That long incubation period makes it difficult to pinpoint exactly when or where you picked up the virus.
Which HPV Types Cause Which Warts
Different strains of HPV tend to target different areas of the body, which is why warts look and behave differently depending on where they appear.
- Common warts (the rough, dome-shaped bumps most often found on fingers, hands, elbows, and knees) are primarily caused by HPV types 2 and 4, though types 1, 3, 7, 27, 29, and 57 can also be responsible.
- Plantar warts (the ones on the soles of your feet that grow inward and can be painful to walk on) come from HPV types 1, 2, 4, 27, and 57. A deeper, more tender variety called a myrmecia is specifically linked to HPV 1, while clusters of smaller, flatter plantar warts (mosaic warts) are typically caused by HPV 2.
- Flat warts (smooth, slightly raised, and often appearing in groups on the face, arms, or legs) are caused by HPV types 3, 10, and 28. These are especially common in children and young adults.
- Filiform warts (thin, finger-like projections that appear on the face, neck, or scalp) and periungual warts (around or under fingernails and toenails) are variants of common warts caused by the same HPV types.
None of these skin-type HPV strains are the same as the sexually transmitted types associated with cervical cancer. They belong to the same virus family but behave very differently.
How the Virus Spreads
HPV spreads through direct skin-to-skin contact with an infected person. The virus enters through breaks in the skin, even tiny ones you can’t see, like hangnails, small scrapes, or areas of dry, cracked skin. Trauma to the skin and prolonged moisture both make it easier for the virus to take hold, which is why warts commonly appear on hands and feet.
Whether you can catch warts from shared surfaces like towels, pool decks, or gym floors is less clear-cut than many people assume. While the idea of picking up plantar warts from a locker room floor is widely repeated, documented transmission through inanimate objects has never been confirmed by the CDC. That said, walking barefoot in warm, wet environments where the virus could survive isn’t doing your feet any favors, especially if you have cuts or cracked skin on your soles.
Spreading Warts to Yourself
One of the most common ways warts multiply on your body is through autoinoculation, which simply means spreading the virus from one spot to another on your own skin. Scratching a wart, then touching another area. Biting your nails when you have a wart on your finger. Shaving over flat warts on your face or legs and dragging the virus across the skin with the razor.
This is why flat warts often appear in lines or clusters along a shaving path. It’s also why periungual warts (around the nails) are more common in people who bite their nails or have jobs that keep their hands constantly wet, like dishwashers or bartenders. Warts on the fingers, elbows, and knees tend to show up in areas subject to repeated friction or minor injury, because those micro-traumas create entry points for the virus.
Who Gets Warts More Easily
Children and teenagers are the most likely to develop warts. Their immune systems haven’t yet built up defenses against the many HPV strains circulating in their environments, and kids are more likely to have the small skin injuries (scraped knees, bitten nails, picked-at cuticles) that let the virus in.
Beyond age, your immune system is the single biggest factor in whether HPV gains a foothold. People with weakened immune systems, whether from an organ transplant, HIV, cancer treatment, or immunosuppressive medications, are significantly more likely to develop widespread warts that are harder to clear. Pregnancy also increases susceptibility, likely due to the immune shifts that occur to protect the developing baby.
Having eczema (atopic dermatitis), particularly when it coexists with asthma or hay fever, is another recognized risk factor. The impaired skin barrier that comes with eczema gives HPV more opportunities to enter, and the chronic inflammation may reduce local immune defenses in the skin.
Why Some Warts Disappear and Others Don’t
Your immune system is ultimately what clears a wart. When your body recognizes the HPV infection and mounts a response, the wart shrinks and eventually falls off on its own. In children, this often happens within a year or two without any treatment. In adults, warts tend to be more stubborn, sometimes lasting years.
The reason some warts persist is that HPV is skilled at hiding from the immune system. The virus stays in the top layer of skin, which has limited blood supply and immune cell traffic. It doesn’t kill the cells it infects or trigger the kind of alarm signals that bring the immune system running. This stealth is also why warts can recur: even after a wart disappears, residual virus in surrounding skin cells can spark a new one, especially if your immune function dips.
People with healthy immune systems who develop one or two warts can generally expect them to resolve, though it may take patience. Those with weakened immunity often need more aggressive treatment because their bodies struggle to mount the response needed to eliminate the virus on their own.