What Can Cause Warts? HPV, Spread, and Risk Factors

Warts are caused by human papillomavirus, or HPV, a family of more than 200 related viruses that infect the skin’s outermost layer. Despite how common they are, the story behind warts is more layered than “you touched something dirty.” Different HPV types produce different kinds of warts, the virus needs broken skin to get a foothold, and whether you actually develop a visible wart depends heavily on your immune system and the degree of exposure you face at home, at school, or even at work.

HPV Is the Only Cause

Every wart, whether it shows up on your finger, the sole of your foot, or the genital area, traces back to an HPV infection. The virus targets keratinocytes, the cells that make up most of your skin’s surface. Research indicates that HPV needs a break in the skin to reach the basal layer of cells where it sets up shop. That wound can be as minor as a hangnail, a scraped knee, or the micro-abrasions you get from walking barefoot on rough concrete.¹ Once inside, the virus hijacks the cell’s normal growth cycle and causes the thickened, rough skin we recognize as a wart.

HPV is remarkably diverse. Different viral types tend to cause warts in different locations and with different appearances. The common wart on your hand may be driven by HPV-2, while a deep, painful plantar wart on the bottom of your foot is more often linked to HPV-1.² Genital warts are associated with still other types, primarily HPV-6 and HPV-11. That distinction matters because knowing the HPV type helps explain why some warts are painful and others barely noticeable, and why treatments that work well in one location may not work the same way elsewhere.

How Warts Spread From Person to Person

HPV transmits through direct skin-to-skin contact with an infected person and through contaminated objects. A systematic review of nonsexual transmission in children identified two strongly associated risk factors: touching the skin of someone who has warts (a classmate, a sibling, a parent) and sharing items like shoes, towels, razors, and bar soap.³ The virus can survive on surfaces long enough to reach the next person who touches them, particularly in warm, damp environments like locker rooms and pool decks.

Genital HPV follows the same basic biology but spreads primarily through sexual contact, including vaginal and anal intercourse. Population studies consistently show high prevalence and high transmissibility, especially among young adults.⁴ The infection can be passed even when no visible wart is present, which is one reason genital HPV is so widespread.

Family and School Exposure Matter More Than Public Pools

There is a popular belief that swimming pools and gym showers are the main places where people pick up warts. The evidence tells a different story. A prospective study of schoolchildren found that having a family member with warts roughly doubled a child’s risk of developing warts, and higher wart prevalence within a school class independently increased each student’s risk as well.⁵ The researchers concluded that preventive efforts should focus more on limiting HPV transmission at home and in classrooms rather than in public facilities.

This makes sense when you think about how much prolonged, close contact families and classmates share compared to the brief exposure you get walking through a swimming pool changing room. Sharing towels every morning, handling the same game controllers, or wrestling with a sibling all create far more opportunity for HPV to jump from one person to another. That does not mean public surfaces are risk-free, but they are not the primary culprit the way many people assume.

Children and Teenagers Are Hit Hardest

Warts peak in prevalence during the second decade of life, affecting more than four in ten children in some studies.⁶ Several factors converge to make young people especially vulnerable. Their immune systems are still learning to recognize and fight HPV. They spend long hours in close contact with other kids at school and in extracurricular activities. And they are more likely to have the kinds of minor skin injuries, from playground scrapes to nail biting, that give the virus an entry point.

The good news is that most childhood warts resolve on their own within months, regardless of treatment.⁶ The immune system eventually mounts an effective response and clears the virus from the skin. That spontaneous resolution is one reason many dermatologists take a watch-and-wait approach with children’s warts unless the wart is painful or causing distress.

Occupational Risks and Butcher’s Warts

One of the more surprising risk factors for warts is working with raw meat. Studies dating back decades have documented unusually high rates of hand warts among butchers, abattoir workers, and other meat handlers. One study found hand wart prevalence of about 33-34% among abattoir workers and butchers, compared with roughly 15% among office workers in the same facilities.⁷ The excess was largely driven by HPV-7, a viral type found almost exclusively in people who handle meat.

What makes this finding unusual is that the researchers could not pin the excess warts on the obvious suspects. Logistic regression analysis showed no link between hand warts and hand trauma, cold and wet working conditions, smoking, atopy, or handling any specific type of meat.⁷ The researchers speculated that something in animal flesh itself may encourage HPV-7 to replicate in human skin. A separate study examining HPV DNA in meat handlers’ warts found the virus in nearly nine out of ten warts tested, with HPV-7 and an unidentified type making up the majority. In most of those patients, warts appeared within two years of starting work with meat, and a potential transmission route through protective gloves and shared equipment was suggested.⁸

Butchers’ warts have their own clinical name and are well recognized in occupational medicine. The mechanism remains genuinely mysterious. HPV-7 does not seem to circulate much outside the meat-handling world, and why raw meat would create a hospitable environment for this particular virus is still an open question.⁹

Your Immune System Is the Deciding Factor

Exposure to HPV is nearly universal over a lifetime, yet not everyone who encounters the virus develops visible warts. The difference comes down to your immune response, specifically the branch of the immune system that relies on specialized cells rather than antibodies. This cell-mediated immune response is responsible for recognizing infected skin cells and clearing HPV from the body. Research has confirmed that this arm of immunity drives the spontaneous regression of warts.¹⁰

When that immune branch is weakened, warts can become extensive and stubbornly resistant to treatment. People living with HIV, organ transplant recipients on immunosuppressive drugs, and patients with certain inherited immune disorders all face significantly higher rates of persistent, widespread warts.¹¹ Dermatologists sometimes use widespread or treatment-resistant warts as a clinical signal that a patient’s immune system deserves closer investigation. The presence of numerous recalcitrant warts in an otherwise healthy-seeming person can point to an undiagnosed immune deficiency.

HPV has also evolved its own strategies to stay hidden from the immune system. The virus replicates inside skin cells without killing them, which means it does not trigger the alarm signals that typically alert immune cells to an infection. It can dampen the production of key immune-signaling molecules and avoid provoking the inflammatory response that would bring immune cells rushing to the site.¹² This stealth is part of why the incubation period from initial infection to a visible wart can range from weeks to many months.

Genetic Conditions That Make Warts Worse

For a small number of people, genes play a direct role in susceptibility to warts. Epidermodysplasia verruciformis is a rare inherited condition in which mutations in genes critical for skin-cell immunity leave patients unable to fight off certain HPV types. The result can be widespread flat warts that persist for life and, in some cases, carry a risk of turning cancerous. Other genetic variants affect T-cell function more broadly, leading to what researchers call “atypical” or “syndromic” forms of the condition.¹³

Researchers have also identified single-gene mutations that can cause otherwise unexplained, severe wart disease. One case study documented a family with an inherited deficiency in a specific immune-signaling molecule (ICOS) where affected members developed stubborn, widespread warts driven by HPV. The discovery illustrated that even a single defect in a gene controlling T-cell cooperation can shift the balance from “occasional mild wart” to “chronic, treatment-resistant disease.”¹⁴ These conditions are rare, but they underscore how tightly wart susceptibility is tied to the immune system’s genetic blueprint.

Latent Virus and Why Warts Come Back

One of the most frustrating things about warts is their tendency to recur even after apparently successful treatment. Research from the 1980s that has held up well over time showed why. When investigators examined apparently normal skin surrounding treated genital warts, they found latent HPV DNA lurking in the margins in nearly half of cases. Among patients whose margins tested positive for the virus, two-thirds experienced recurrence, compared with less than one in ten patients whose margins were virus-free.¹⁵

This means the virus can persist in skin that looks and feels completely normal, well beyond the borders of the wart you can see. Freezing, burning, or cutting off a visible wart removes the visible lesion but may leave behind a reservoir of virus in surrounding tissue. That reservoir, held in check by the immune system but not fully eliminated, can reactivate weeks or months later. The phenomenon applies to cutaneous warts as well, not just genital ones, and is a major reason why recurrence rates for wart treatment remain frustratingly high across methods.

Everyday Prevention

Because HPV enters through broken skin and spreads by contact, the most effective prevention strategies are mundane but worthwhile. Avoid touching someone else’s warts directly. Do not share towels, razors, nail clippers, or socks with a person who has active warts. Keep your own warts covered with a bandage to reduce shedding virus onto surfaces and other people. In wet communal areas like pool decks or shared showers, wearing flip-flops adds a layer of protection, though the evidence suggests that family and close-contact settings are bigger transmission risks than these public spaces.

For genital HPV, the quadrivalent and newer HPV vaccines offer strong protection against the types that cause most genital warts. One small exploratory study even found that giving the quadrivalent vaccine to patients with existing recurrent genital warts led to high response rates and no recurrences during follow-up in the vaccinated group, suggesting the vaccine may have some therapeutic potential beyond its established preventive role.¹⁶ Vaccination before first exposure remains the most effective approach, which is why public health guidelines recommend it during adolescence.

The Psychological Weight of Warts

Warts are often treated as trivial, a cosmetic nuisance at worst. But research into quality of life tells a different story, especially for genital warts. A study of patients with anogenital warts found that despite being only mildly symptomatic physically, the disease carried a considerable negative psychological burden, affecting self-image, sexual confidence, and relationships.¹⁷

The psychological toll is not limited to genital warts. A comparative study found that warts on the hands, feet, and face also inflicted a severe negative impact on quality of life in adults with healthy immune systems. The persistence and recurrence of warts amplified the distress, as patients dealt with repeated treatments and the social embarrassment of visible lesions.¹⁸ These findings have pushed some dermatologists to incorporate discussions of mental well-being into wart consultations, rather than treating the problem as purely physical.

An Ancient Virus With a Long History

HPV is not some modern pathogen that appeared alongside crowded cities or industrial farming. Papillomaviruses are ancient, with evolutionary histories stretching back hundreds of millions of years alongside their host species. Researchers tracing the origins and evolution of papillomavirus genes have assembled a timeline showing that these viruses have diversified alongside vertebrates over deep evolutionary time, accumulating genetic innovations along the way.¹⁹ The sheer number of HPV types that infect humans, over 200, reflects this long co-evolution: the virus has had eons to specialize in different tissues and ecological niches on our bodies.

That evolutionary depth also explains some of HPV’s more exasperating qualities. The virus’s ability to hide from the immune system, persist in latent form, and exploit the skin’s normal wound-healing process are not accidents. They are the product of millions of years of arms-race refinement between virus and host. Understanding warts as the product of this deep evolutionary relationship puts the stubbornness of the infection in perspective: you are dealing with a pathogen that has been perfecting its strategy for far longer than humans have existed.