Warts are caused by the human papillomavirus, commonly known as HPV. The virus infects the outermost layer of skin through tiny breaks or cuts, then triggers the skin cells to multiply rapidly, producing the rough, raised growth you see on the surface. There are over 100 strains of HPV, and different strains tend to cause warts in different locations on the body.
How HPV Gets Into Your Skin
HPV needs an entry point. It can’t penetrate intact, healthy skin on its own. Instead, it slips through microscopic breaks in the skin barrier, the kind you’d get from a small cut, a hangnail, a scrape, or even the friction of biting your nails. People with conditions like eczema that compromise the skin barrier are at higher risk for this reason.
Once inside, the virus targets cells in the deepest part of the outer skin layer called the basal layer. It hijacks those cells and causes them to reproduce far faster than normal, stacking up into a thick, hardened bump. That overgrowth of skin cells is the wart itself. The virus also produces infectious particles within the wart, which is why warts can spread so easily.
How Warts Spread
Warts are contagious. You can pick up HPV through direct skin-to-skin contact with someone who has a wart, or indirectly through contaminated surfaces and objects. Towels, razors, nail clippers, and salon tools can all carry the virus. HPV is surprisingly durable outside the body: it retains about 50% of its ability to infect after sitting on a dry surface for three days at room temperature.
You can also spread warts to yourself, a process called autoinoculation. Scratching or picking at a wart, then touching another part of your body, can deposit the virus in a new location. Shaving is a common culprit. Dragging a razor over a wart and then across unaffected skin creates both a source of virus and the tiny skin breaks it needs to establish a new infection. This is why warts sometimes appear in clusters or lines along the path of a razor.
Walking barefoot in warm, damp environments like pool decks and locker rooms is a classic way to pick up plantar warts on the soles of your feet. The moisture softens the skin, making it easier for the virus to penetrate.
Different Strains Cause Different Warts
Not all warts look the same, and that’s partly because different HPV strains target different areas of the body. Common warts, the firm, dome-shaped bumps that typically show up on fingers and hands, are most often caused by HPV types 2 and 4. Plantar warts on the soles of the feet are usually caused by HPV type 1. Flat warts, which are smoother, smaller, and tend to appear in large numbers on the face, arms, or legs, are linked to HPV types 3, 10, and 28.
These are all different from the HPV strains associated with genital warts or cervical cancer. The strains that cause common skin warts are generally low-risk and don’t lead to cancer.
Who Gets Warts More Easily
Children and teenagers get warts more often than adults, likely because their immune systems haven’t yet built up defenses against the many strains of HPV circulating in schools, playgrounds, and swimming pools. Most adults develop some degree of immunity over time through repeated exposure.
Your immune system plays a central role in whether HPV takes hold and how long a wart sticks around. People with weakened immune systems, whether from medications that suppress immune function, organ transplantation, or HIV, tend to develop more warts that are harder to get rid of. Children with eczema also face a higher risk because their damaged skin barrier gives the virus easier access.
In rare cases, people who develop unusually widespread or persistent warts that don’t respond to treatment may have an underlying genetic immune deficiency. Several inherited conditions make the body specifically vulnerable to HPV. One example is WHIM syndrome, named in part for the warts it causes. Another is a condition called epidermodysplasia verruciformis, where patients are extremely susceptible to HPV strains that would normally never cause problems in a healthy person. These are uncommon, but doctors may investigate them when warts are severe and don’t respond to standard treatments.
How Long Before a Wart Appears
One of the tricky things about warts is the delay between infection and the appearance of a visible bump. The incubation period varies widely, averaging around 3 months but sometimes stretching much longer. This lag makes it nearly impossible to pinpoint exactly when or where you picked up the virus. By the time you notice a wart on your hand, the exposure could have happened months earlier from a surface or contact you’ve long forgotten about.
Do Warts Go Away on Their Own
Many warts do eventually clear without treatment as the immune system recognizes and fights off the virus. This is especially true in children. The catch is that “eventually” can mean months or even years. Some warts disappear within a year, while others persist for two years or longer. During that time, they can spread to new areas or to other people.
Over-the-counter treatments containing salicylic acid work by peeling away the infected skin layer by layer. Freezing (cryotherapy) at a doctor’s office destroys the wart tissue. Both approaches often require multiple rounds over several weeks. Plantar warts tend to be the most stubborn because they grow inward under the pressure of body weight, making them harder to reach.
Limiting the Spread
Since warts spread through contact and tiny skin injuries, a few practical habits make a real difference. Avoid picking at or scratching existing warts, because even minor trauma can scatter the virus to new spots. Don’t share razors, towels, or nail clippers with someone who has warts, and replace your own razor if you’ve shaved over a wart. Wear sandals or flip-flops in communal showers and around pools.
If you’re getting a haircut, threading, or any cosmetic procedure that involves blades or tools near the skin, fresh instruments matter. Reused threads, blades, or unsanitized tools in salons have been documented as a source of wart transmission. Keeping existing warts covered with a bandage during activities where skin contact is likely, such as sports, reduces the chance of passing the virus to someone else.