Warts are caused by the human papillomavirus, or HPV, which infects skin cells through tiny cuts or breaks in the skin’s surface. There are over 100 types of HPV, and different strains cause warts in different locations on the body. The virus is remarkably common, and most people will develop at least one wart at some point in their lives.
How HPV Gets Into Your Skin
HPV can’t penetrate healthy, intact skin. It needs a way in. When you get a small cut, scrape, or even a micro-abrasion you can’t see, the outermost barrier of your skin breaks open and exposes a deeper layer called the basement membrane. The virus latches onto proteins in this exposed layer and waits there while skin cells migrate inward to close the wound. As those healing cells move across the damaged area, the virus hitches a ride into the deeper layers of skin where it can set up a long-term infection.
Once inside, HPV targets the basal cells at the base of your outer skin layer. These are the cells that divide and push new skin cells toward the surface. The virus reprograms them to multiply faster than normal and to keep dividing even in layers of skin where cells would typically stop growing. The result is a dense mound of thickened, roughened skin: a wart. That characteristic hard, bumpy texture comes from the overproduction of the tough protein that makes up your skin’s outermost layer.
Different Strains, Different Warts
Not all warts look the same because different HPV types behave differently in skin cells. The strain that infects you determines where the wart appears and what it looks like.
- Common warts (rough, dome-shaped bumps usually on hands and fingers) are most often caused by HPV types 2 and 4, though types 1, 3, 27, 29, and 57 can also be responsible.
- Plantar warts (hard, flat growths on the soles of the feet) are most commonly caused by HPV type 1, followed by types 2, 3, 4, 27, and 57.
- Flat warts (small, smooth, slightly raised bumps that often appear in clusters on the face or legs) are caused by HPV types 3, 10, and 28.
- Genital warts are a separate category entirely. About 90% are caused by HPV types 6 or 11, which are different from the strains that cause skin warts. The HPV types responsible for genital warts are also different from the types linked to cancer.
How Warts Spread From Person to Person
Skin warts spread through direct contact with the virus. You can pick it up by touching someone else’s wart, but indirect contact is just as common. Walking barefoot on a wet locker room floor, sharing towels, or gripping gym equipment that someone with a hand wart has used can all transfer the virus. HPV thrives in warm, moist environments, which is why communal showers and pool decks are well-known hotspots for plantar warts.
Genital warts spread through sexual contact, including vaginal, anal, and oral contact. The virus can be transmitted even when no visible warts are present, which makes it easy to pass along unknowingly.
How You Spread Warts to Yourself
One of the most frustrating things about warts is how easily you can spread them from one part of your body to another. This process, called auto-inoculation, happens when virus particles from an existing wart get deposited on a new area of broken skin.
Shaving is one of the most common culprits. Dragging a razor over a flat wart on your leg scrapes virus particles across every tiny nick the blade creates, seeding new warts along the shaving path. Scratching a wart and then scratching another part of your body can do the same thing if your fingernail carries enough viral material to a fresh break in the skin.
Nail biting creates a particularly unfortunate pattern. People with warts on their fingers who bite at them often end up transferring the virus to their lips, resulting in warts in both locations. Any habit that involves picking at a wart and then touching other skin increases the risk of spreading it.
Why Some People Get Warts More Easily
Children are especially prone to warts, partly because their immune systems haven’t yet encountered HPV and partly because kids tend to get more scrapes and cuts that give the virus easy entry points. Most childhood warts eventually resolve as the immune system learns to recognize and fight the virus.
People with weakened immune systems face a much harder time. Those with HIV or anyone taking immunosuppressive medications (such as organ transplant recipients) often develop more numerous, larger, and more stubborn warts. Their immune systems struggle to keep the virus in check, which allows HPV to persist longer and spread more aggressively. In these populations, warts can become widespread and respond poorly to treatment.
Even among otherwise healthy adults, individual immune response plays a role. Some people seem to clear HPV quickly and rarely develop visible warts, while others are more susceptible. The reasons aren’t fully understood, but the strength of your cell-mediated immune response (the branch of your immune system that attacks virus-infected cells) appears to be the key factor.
How Long Warts Take to Appear
Warts don’t show up right away. After exposure to HPV, the incubation period ranges from 1 to 20 months, with most warts appearing around 2 to 3 months after infection. This long delay makes it nearly impossible to pinpoint exactly when or where you picked up the virus. You might develop a wart on your hand months after the gym session that caused it, with no memory of the exposure.
This slow timeline also explains why warts sometimes seem to appear out of nowhere. The virus can sit in skin cells for weeks or months before triggering enough abnormal cell growth to produce a visible bump.
Do Warts Go Away on Their Own?
Many warts do clear without treatment, but the timeline varies widely. In healthy people, the immune system gradually recognizes the infected cells and mounts a response that destroys the wart from within. This process can take months to a couple of years, and there’s no reliable way to predict how long a specific wart will last.
Some warts persist for years, especially plantar warts and warts in people with compromised immunity. Treatment options like cryotherapy (freezing), salicylic acid, and other approaches work by either destroying the infected tissue or triggering a stronger local immune response. Even with treatment, warts can recur because the virus may linger in surrounding skin cells that appear normal.
Does the HPV Vaccine Prevent Skin Warts?
The HPV vaccine was designed to prevent genital warts and HPV-related cancers by targeting HPV types 6, 11, 16, 18, and five additional high-risk strains. It was not designed to protect against the HPV types that cause common skin warts. Some researchers have speculated that the vaccine’s immune response might cross-react with related strains, but clinical evidence so far has not shown a significant effect on clearing or preventing cutaneous warts. Randomized controlled trials would be needed before any broader recommendations could be made.