Warts are caused by the human papillomavirus (HPV), which enters your skin through tiny cuts, scrapes, or breaks you may not even notice. The virus infects the deepest layer of your outer skin, where it hijacks cells and causes them to multiply rapidly, forming the raised, rough growths you see on the surface. Warts are extremely common, particularly in children, affecting roughly one in three school-aged kids at any given time.
How HPV Gets Into Your Skin
HPV needs a way past your skin’s outer barrier. It finds that entry point through micro-abrasions: tiny nicks, cracks, or breaks in the skin that are often invisible to the naked eye. Once the virus reaches the basal layer of your epidermis (the deepest part of your outer skin), it attaches to receptors on cell surfaces and releases its DNA into the cell. From there, it forces those cells to replicate faster than normal, eventually producing a wart.
This is why warts tend to show up in areas prone to minor damage. Hands get scraped and nicked constantly. Feet endure friction from shoes and rough surfaces. Bitten nails and torn cuticles create perfect entry points around the fingertips. Dry, cracked skin anywhere on the body is also more vulnerable, because those cracks act as open doors for the virus.
Direct Contact and Surface Transmission
You can pick up HPV two ways: touching a wart directly or touching a surface the virus has landed on. Skin-to-skin contact is the most straightforward route. If you shake hands with someone who has a wart on their finger, or your foot brushes against someone else’s plantar wart at a pool, the virus can transfer to any break in your skin.
Indirect transmission is just as real. HPV thrives in warm, moist environments and can survive on surfaces for several months. Pool decks, locker room floors, communal showers, and shared towels are all common culprits. This is why plantar warts on the feet are so closely associated with swimming pools and gym facilities.
Spreading Warts to Yourself
One of the most common ways warts multiply is autoinoculation, which simply means spreading the virus from one part of your body to another. Picking at a wart, biting your nails, or chewing your cuticles are especially effective at doing this, because the act creates fresh breaks in the skin while simultaneously exposing those breaks to the virus. Shaving over or near a wart can drag viral particles across a wide area of skin, which is why warts sometimes appear in clusters along a shaving path. If you have a wart, washing your hands after touching it makes a meaningful difference in keeping it from spreading.
Why Some People Get Warts and Others Don’t
Not everyone exposed to HPV develops a visible wart. Your immune system, specifically the branch that uses specialized white blood cells to hunt down infected cells, determines whether the virus takes hold or gets cleared before a wart ever forms. HPV has evolved a clever trick: it delays producing its most recognizable proteins until cells have migrated to the outermost, dying layer of skin, where immune cells have less access. This helps the virus hide from your immune system long enough to establish itself.
People with weakened immune systems are at significantly higher risk. Organ transplant recipients on anti-rejection medications develop warts at striking rates: 50 to 90 percent of transplant patients have warts within four to five years of starting immunosuppressive therapy. People living with HIV and those with rare inherited immune conditions also face a much higher burden of warts. Even everyday factors like stress, fatigue, or illness that temporarily suppress immune function can tip the balance in the virus’s favor.
Age and Other Risk Factors
Children are far more likely to get warts than adults. A Dutch study of nearly 1,500 schoolchildren found that wart prevalence jumped from 15 percent in four-year-olds to 44 percent in eleven-year-olds. Over 40 percent of children develop warts during their school years. This likely reflects a combination of immature immune systems, frequent skin-to-skin contact during play, and less consistent hygiene habits. Wart prevalence drops substantially in adulthood. One study of over 15,000 college students found a rate of just 1.4 percent.
Excessive sweating (hyperhidrosis) is another risk factor. Persistently damp, softened skin is more permeable to HPV. People with eczema or other conditions that compromise the skin barrier are similarly more susceptible.
The Delay Between Exposure and Appearance
One reason warts seem to appear out of nowhere is the long incubation period. After HPV enters your skin, it typically takes two to three months before a visible wart develops. In some cases, warts can take up to 20 months to appear. This means the wart on your hand today may trace back to a handshake, a gym session, or a scraped knuckle from half a year ago. The delay makes it nearly impossible to pinpoint exactly when or where you picked up the virus.
Types of Warts and Where They Appear
The specific strain of HPV you encounter influences what kind of wart develops and where. HPV types 1, 2, 4, 27, and 57 are the strains responsible for skin warts. Different strains tend to favor different body sites, producing distinct wart types:
- Common warts appear mostly on the hands as rough, dome-shaped bumps ranging from pinhead to pea-sized. They often have tiny black dots, which are clotted blood vessels rather than “seeds.”
- Plantar warts grow on the soles of the feet and tend to be flat or grow inward because of the pressure from standing and walking. They can become large and painful.
- Flat warts are smaller and smoother than other types and can appear anywhere on the body. They tend to show up in clusters of 20 to 100 at a time.
- Filiform warts look like long, thin threads projecting from the skin. They favor the face, growing around the mouth, eyes, and nose.
In schoolchildren with warts, about 59 percent have only plantar warts, while 13 percent have warts on both the hands and feet.
Practical Ways to Lower Your Risk
You can’t guarantee you’ll never encounter HPV, but you can reduce the chances it gets through your skin. Wearing flip-flops or pool shoes in locker rooms, around pools, and in public showers removes the most common exposure point for plantar warts. Keeping cuts and scrapes clean and covered denies the virus easy entry. Moisturizing dry or cracked skin, particularly on your hands and feet during winter, helps maintain your skin’s barrier function.
If you already have a wart, avoiding picking or scratching it is the single most effective way to stop it from spreading. Breaking a nail-biting habit can prevent warts from establishing around the fingertips. And if you shave near a wart, use caution or switch to a method that doesn’t drag a blade across the affected skin.