Warts are caused by human papillomavirus, or HPV, which infects skin cells after slipping through tiny breaks in the outer layer of skin. Whether you actually develop a visible wart after exposure comes down mostly to how your immune system handles the virus. Some people’s defenses stamp out the infection before it ever produces a bump, while others mount a slower or weaker response that lets the virus set up shop and force skin cells to overgrow into the rough, raised lumps we recognize as warts.
How the Virus Gets In
HPV is not a single virus but a large family. More than 200 types have been identified, and the ones responsible for common skin warts are a relatively narrow set. The types most frequently found in cutaneous warts include HPV 2, 27, and 57, along with HPV 4 and HPV 1. Different types tend to favor different locations on the body. HPV 1, for instance, shows a distinct preference for the soles of the feet and is especially common in children under twelve with warts that have been present for less than six months.1PubMed. Cutaneous wart-associated HPV types: prevalence and relation with patient characteristics
The virus enters the skin through microtrauma, the kind of damage so small you would never notice it. A scraped knee, a hangnail, the imperceptible cracks that form on dry heels or fingers in winter, or the wear on the soles of your feet from walking barefoot on rough pool decks. Once inside, HPV targets the basal cells at the bottom of the epidermis. It does not enter the bloodstream or spread through the body the way a cold virus does. It stays local, hijacking the cell’s machinery to reproduce itself as the skin cell divides and migrates upward.
Transmission happens through direct skin-to-skin contact with someone who has warts and through contaminated surfaces. A systematic review of pediatric wart transmission found two strongly associated risk factors: contact with affected individuals (classmates, siblings, family members) and shared objects like shoes, towels, razors, and bar soap.2PubMed. Systematic Review of the Epidemiology and Risk Factors for Nonsexual Transmission of Warts and Molluscum in Children Swimming pools and shared showers also appear on the list, likely because wet skin softens and develops microtears more easily, and because the virus can survive briefly on warm, moist surfaces.
Why Your Immune System Is the Real Decider
If HPV exposure were all it took, nearly everyone would be walking around covered in warts. The virus is extremely common in the environment, yet plenty of people never develop a single wart despite presumably encountering it. The difference lies in the immune response, specifically the branch of immunity that hunts down and destroys infected cells rather than the branch that makes antibodies.
Cell-mediated immunity, the arm of the immune system driven by T cells, plays the central role in controlling HPV. Clinical evidence has shown this for decades: the incidence of warts climbs sharply in people receiving immunosuppressive drugs and in those with diseases that impair T-cell function, such as certain blood cancers.3Clinics in Dermatology. Cell-mediated immunity to human papillomavirus Among people who do get warts, those whose immune systems respond within the first year tend to clear the infection, whereas people whose warts persist beyond a year often show weaker immune reactivity to the virus.4PubMed Central. Cell-mediated immunity to human wart virus and wart-associated tissue antigens This protective immunity appears to be relatively short-lived, which helps explain why someone can clear warts once and then develop them again years later.
Your body has a first-line defense even before T cells get involved. Small antimicrobial proteins called defensins, produced by immune cells and by the skin’s own epithelial cells, can directly block papillomavirus from infecting cells. Lab research has shown that certain human alpha-defensins are potent antagonists of both cutaneous and mucosal HPV types.5PubMed Central. Human alpha-defensins block papillomavirus infection Another antimicrobial peptide, cathelicidin, has been shown in mouse models to protect against papillomavirus skin infection, not just by attacking the virus directly but by boosting the broader immune response.6PubMed Central. Deficiency of Cathelicidin-related Antimicrobial Peptide Promotes Skin Papillomatosis in Mus musculus Papillomavirus 1-infected Mice People whose skin produces more of these peptides at baseline likely have a built-in advantage against HPV establishing itself.
How HPV Hides from Your Defenses
HPV has had a very long time to figure out how to avoid human immune detection. The virus and its primate ancestors have been co-evolving with us for tens of thousands of years or more.7PubMed Central. Ancient Evolutionary History of Human Papillomavirus Type 16, 18 and 58 Variants Prevalent Exclusively in Japan That evolutionary pressure has produced a virus remarkably good at staying invisible to immunity.
HPV confines its entire life cycle to the upper layers of the skin, a tissue with relatively little immune surveillance compared to, say, your blood or lymph nodes. The virus does not kill the cells it infects, so there is no inflammatory alarm signal of the kind that a lytic virus would trigger. It keeps its protein production to a minimum in the deeper cell layers where immune cells patrol, only ramping up virus production in the outermost cells that are about to be shed from the skin surface anyway. By the time the virus is being assembled in large quantities, it is essentially already on its way out the door. Multiple immune evasion strategies have been documented, all oriented around the same basic principle: HPV needs time in the skin to complete its reproductive cycle, so it has evolved to stay quiet long enough to do so.8PubMed Central. The invisible enemy – how human papillomaviruses avoid recognition and clearance by the host immune system
This stealth is a big part of why some people develop warts while others seem immune. It is not necessarily that one person’s immune system is “stronger” in a general sense. It may be that one person’s immune cells happen to detect the subtle signals HPV gives off while another person’s do not, at least not quickly enough. The window between viral entry and an effective immune response determines whether a wart forms or the infection is silently eliminated.
Children, Teenagers, and the Age Factor
Warts are disproportionately a childhood phenomenon. In the general population, they affect a sizable percentage of school-age kids, with the infection most common in the second decade of life, affecting over 40% of children.9PubMed Central. Paediatric Cutaneous Warts and Verrucae: An Update Population-level data from the United States shows that the prevalence of warts rises steadily from early childhood, peaks around ages nine to ten, then plateaus through the teenage years.10Journal of Investigative Dermatology. The US Prevalence of Common Warts in Childhood: A Population-Based Study
Several factors converge to make kids especially vulnerable. Their immune systems are still being educated. Every encounter with a new pathogen is the first encounter, and building a robust cell-mediated response takes time. Children are also in close physical contact with each other constantly, sharing objects in classrooms, playing in ways that create small skin injuries, and often walking barefoot in communal spaces like pools and locker rooms. The decline in wart prevalence as people move into adulthood likely reflects accumulated immune experience: adults who have already fought off HPV carry some degree of immune memory, even if that memory is imperfect.
When Genetics Tip the Scales
Most of the variation in wart susceptibility comes from normal differences in immune function. But genetics can push things to an extreme. The starkest example is a rare inherited condition called epidermodysplasia verruciformis, in which people develop widespread, persistent wart-like lesions caused by HPV types that most people carry on their skin without ever knowing it. This condition results from mutations in genes called TMC6 (also known as EVER1) and TMC8 (EVER2), or in a gene called CIB1.11PLOS Pathogens. MmuPV1 infection of Tmc6/Ever1 or Tmc8/Ever2 deficient FVB mice as a model of βHPV in typical epidermodysplasia verruciformis Research has confirmed that pathogenic variants in TMC6 or TMC8 can be identified in affected patients, providing molecular proof of the genetic basis.12European Journal of Human Genetics. TMC6/8-associated epidermodysplasia verruciformis: germline variants and a complex structural alteration in a skin cancer predisposition syndrome
These genes encode proteins involved in regulating zinc distribution inside skin cells, which in turn affects the cell’s ability to fight viral infection. When both copies of the gene are nonfunctional, the immune system essentially loses its ability to control certain HPV types, leading to lifelong warty growths and a significantly increased risk of skin cancer in sun-exposed areas. The condition is rare, but it illustrates a principle that probably applies more broadly in milder forms: subtle genetic variation in immune-related genes likely contributes to why one family member seems to catch warts easily while another never does, even under the same exposure conditions.
Skin Conditions That Open the Door
Your skin itself is a barrier, and when that barrier is compromised, HPV has an easier time getting in. Children with atopic dermatitis, the most common type of eczema, appear to be more susceptible to warts. A large US population-based study found that childhood eczema and warts are associated with increased risk of infections, suggesting that barrier disruption, immune disruption, or both contribute to wart susceptibility.13PubMed. Childhood atopic dermatitis and warts are associated with increased risk of infection: a US population-based study
One might expect that specific genetic skin-barrier defects, like mutations in the filaggrin gene that cause dry, crack-prone skin, would independently raise wart risk. But at least one study found no association between filaggrin mutations and wart treatments in children.14PubMed. Filaggrin genotype and skin diseases independent of atopic dermatitis in childhood The link between eczema and warts may have more to do with the chronic inflammation and immune imbalance that eczema creates than with the physical dryness of the skin alone. Eczema tends to shift the immune response in a direction that favors allergic reactions over antiviral defenses, which could give HPV an advantage.
Why Warts Disappear on Their Own
One of the more puzzling things about warts is that they often vanish without any treatment. This spontaneous regression is not random or mysterious; it is an active immune process. Researchers examining warts in the process of disappearing have found that the tissue is flooded with T lymphocytes, which migrate into the wart and attack the virus-infected skin cells directly. The process looks a lot like the immune system’s rejection of a foreign graft.15PubMed. Primary tissue culture of spontaneously regressing flat warts. In vitro attack by mononuclear cells against wart-derived epidermal cells
Detailed analysis of regressing flat warts has shown that the immune cells involved are a mix of helper T cells in the surrounding skin and both helper and killer T cells invading the wart itself. Many of these T cells show markers of activation, indicating they are actively working. The HPV viral protein that can be detected in the nuclei of cells in non-regressing warts disappears from regressing ones, suggesting the immune attack is effective at eliminating both the infected cells and their viral cargo.16PubMed. Immunohistologic analysis of the phenomenon of spontaneous regression of numerous flat warts The evidence points strongly to cell-mediated destruction of virus-infected skin cells, rather than a direct antiviral attack, as the mechanism behind spontaneous wart regression.17Archives of Dermatology. Plane Warts Under Spontaneous Regression: Immunopathologic Study on Cellular Constituents Leading to the Inflammatory Reaction
When regression happens, it often happens to all of a person’s warts at once rather than one at a time, which supports the idea that the body mounts a systemic immune response rather than fighting each wart individually. The timing varies wildly. Some warts disappear within months; others stick around for years before the immune system finally catches up.
Latency and Why Warts Recur
Even after warts have cleared, either on their own or after treatment, the virus does not always leave. In animal models where researchers have looked carefully, papillomavirus DNA can be found at sites of previous infection long after the visible wart has gone, lurking in the basal cell layer of the skin.18PubMed Central. The biology of papillomavirus latency This viral persistence without visible disease is why warts so commonly recur, sometimes in the exact same spot.
The concept of HPV “clearance” is increasingly being questioned by researchers. What looks like the virus being eliminated may actually be the virus being suppressed to a level below what produces symptoms, maintained in check by ongoing immune surveillance. One review argued that the terms “apparent clearance” and “subclinical persistence” more accurately describe what is happening than true viral eradication.19PubMed Central. The human Papillomavirus twilight zone – Latency, immune control and subclinical infection If your immune system weakens for any reason, whether from illness, medication, aging, or stress, latent HPV can reactivate and produce new warts. This helps explain why immunosuppressed patients, such as organ transplant recipients on anti-rejection drugs, develop persistent and widespread warts that resist standard treatments.20PubMed Central. Recalcitrant hyperkeratotic verrucae in a renal transplant recipient clearing with cessation of immunosuppression
How Stress Plays Into It
The connection between stress and warts is not just folk wisdom. Psychological stress has measurable effects on the immune pathways that control HPV. Stress hormones can reactivate latent tumor viruses, stimulate viral gene expression, and suppress antiviral immune responses. In people fighting HPV, immune regression of lesions is associated with increased activity from a particular subset of T cells. During periods of sustained psychological stress, that subset’s activity drops, shifting the balance in a direction that favors the virus rather than the host.21PubMed. The Influence of Psychological Stress on HPV Infection Manifestations and Carcinogenesis
This does not mean that stress causes warts in the way a virus does. It means stress can tip the balance: making it harder for your body to suppress an infection it has already acquired, prolonging the duration of existing warts, or creating an opening for latent HPV to resurface. It is one more variable in the complex equation that determines whether any given person develops visible warts at any given time.
What Treatments Actually Accomplish
Given that warts are maintained by the immune system’s inability (or delayed ability) to eliminate infected cells, you would expect the most effective treatments to be the ones that either destroy the infected tissue or provoke an immune response. In practice, the two most common over-the-counter and clinical treatments do the former.
Salicylic acid, applied topically, works by chemically dissolving the layers of thickened, virus-containing skin. Cryotherapy with liquid nitrogen freezes and destroys the wart tissue. A meta-analysis comparing the two for common warts found no statistically significant difference in complete clearance at twelve weeks.22Dermatologic Therapy. Comparison of Cryotherapy and Topical Salicylic Acid in Common Warts: A Systematic Review and Meta‐Analysis However, one randomized trial found that location matters. For common warts on the hands and elsewhere, cryotherapy cleared about half of cases compared to roughly 15% with salicylic acid and 8% with no treatment. But for plantar warts on the soles of the feet, cure rates did not differ significantly between treatment groups, and both were modest.23PubMed Central. Cryotherapy with liquid nitrogen versus topical salicylic acid application for cutaneous warts in primary care: randomized controlled trial A separate trial looking specifically at plantar warts found only about a 14% clearance rate in both groups at twelve weeks.24PubMed Central. Cryotherapy versus salicylic acid for the treatment of plantar warts (verrucae): a randomised controlled trial
These modest numbers reflect an uncomfortable truth: destroying the physical wart does not eliminate the virus from the surrounding skin. That is why recurrence is so common after treatment. Some dermatologists have turned to immunotherapy approaches that try to wake up the immune system rather than just burn or dissolve the wart away. One technique involves injecting an unrelated antigen, like mumps or Candida skin-test extract, directly into the wart. The resulting immune flare-up at the injection site appears to finally alert T cells to the presence of HPV, sometimes clearing not just the injected wart but distant warts on other parts of the body.25Archives of Dermatology. Intralesional Injection of Mumps or Candida Skin Test Antigens: A Novel Immunotherapy for Warts The logic is elegant: the virus has been hiding from the immune system, and the injection effectively forces the immune system to pay attention to that particular patch of skin.
When a Wart Is Not a Wart
A practical concern worth knowing about: not every bump that looks like a wart is actually one. A study collecting lesions that were clinically diagnosed as warts before closer examination found a range of other conditions masquerading as warts. The most common mimics were molluscum contagiosum (caused by a completely different virus), calluses, and seborrheic keratoses, a type of benign age-related skin growth. Less commonly, the list included skin tags, certain benign tumors, corns, and in a small number of cases, squamous cell carcinoma and Bowen’s disease, both of which are forms of skin cancer.26Our Dermatology Online. Warts or mimickers? The essential role of dermoscopy in improving diagnostic accuracy
The practical takeaway: if you have a persistent bump that has not responded to standard wart treatment, or if it looks unusual, bleeds easily, or is growing in a way that seems off, it is worth having a dermatologist look at it with a dermatoscope rather than continuing to treat it as a wart at home. Most bumps will be harmless, but the small overlap with skin cancers means that a confident diagnosis matters more than people tend to assume.