# Human Papillomavirus: Warts, Condylomata, and Oncogenic Risk
## Overview
Human papillomaviruses (HPVs) are a large family of non-enveloped, double-stranded DNA viruses with tropism for squamous epithelium. Over 200 HPV types have been identified, causing a spectrum from benign warts to premalignant and malignant lesions. Understanding oncogenic risk stratification and available treatments is essential for dermatologic practice.
## Virology
HPV is a non-enveloped, double-stranded circular DNA virus with an approximately 8 kb genome. It infects basal keratinocytes through microabrasions, and its viral life cycle is tightly linked to keratinocyte differentiation. The virus does not cause viremia; infection remains local. Key viral proteins include E6 and E7, the oncoproteins (E6 degrades p53 and E7 inactivates the retinoblastoma protein), E1 and E2 (involved in viral replication), and L1 and L2, the capsid proteins (L1 is the target of prophylactic vaccines).
## HPV Type Classification
### Low-Risk Types (Non-Oncogenic)
| Risk Category | HPV Types | Clinical Association |
|---|---|---|
| Low-risk | 6, 11 | Anogenital warts (condylomata acuminata), laryngeal papillomatosis |
| Low-risk | 1 | Deep plantar warts (myrmecia) |
| Low-risk | 2, 4 | Common warts (verruca vulgaris) |
| Low-risk | 3, 10 | Flat warts (verruca plana) |
| High-risk | 16 | Cervical, penile, anal, oropharyngeal SCC (most common oncogenic type) |
| High-risk | 18 | Cervical adenocarcinoma |
| High-risk | 31, 33, 45, 52, 58 | Additional oncogenic types |
| EV-associated | 5, 8 | SCC in epidermodysplasia verruciformis |
HPV 6 and 11 cause condylomata acuminata (anogenital warts) and laryngeal papillomatosis. HPV 1 causes deep plantar warts (myrmecia). HPV 2 and 4 cause common warts (verruca vulgaris). HPV 3 and 10 cause flat warts (verruca plana).
### High-Risk Types (Oncogenic)
HPV 16 is the most common oncogenic type, associated with cervical, penile, anal, and oropharyngeal squamous cell carcinoma. HPV 18 is particularly associated with cervical adenocarcinoma. Additional high-risk types include HPV 31, 33, 45, 52, and 58. HPV 5 and 8 are associated with SCC in epidermodysplasia verruciformis.
## Clinical Presentations
### Verruca Vulgaris (Common Warts)
Common warts present as hyperkeratotic, papillomatous, dome-shaped papules, most commonly on the hands and fingers. "Black dots" on the surface represent thrombosed capillaries, not "seeds." Disruption of normal dermatoglyphics (fingerprint lines interrupted) is a key diagnostic feature. Koebnerization (spread along lines of trauma) is common. Spontaneous resolution occurs in 60 to 65 percent of cases within two years through immune-mediated clearance.
### Verruca Plantaris (Plantar Warts)
Plantar warts show endophytic growth due to weight-bearing pressure and are painful on lateral compression, unlike calluses which are painful on direct pressure. Myrmecia (deep plantar wart from HPV 1) is single, deep, and painful, while mosaic warts (HPV 2) are coalesced superficial plantar warts. Disruption of dermatoglyphics distinguishes plantar warts from calluses or corns.
### Verruca Plana (Flat Warts)
Flat warts are small (2 to 4 mm), flat-topped, slightly elevated, skin-colored to tan papules found on the face, dorsal hands, and shins. They are caused by HPV 3, 10, and 28. Often dozens to hundreds of lesions are present, with prominent Koebner phenomenon producing a linear distribution from scratching. They may resolve with transient inflammation ("wart flare").
### Condylomata Acuminata (Anogenital Warts)
Anogenital warts present as soft, papillomatous, flesh-colored to pink papules and plaques in the genital, perianal, and inguinal areas. HPV 6 and 11 account for more than 90 percent of cases. They are sexually transmitted with an incubation period of 3 weeks to 8 months. Giant condylomata of Buschke-Lowenstein are large, locally destructive verrucous carcinomas associated with HPV 6 and 11. In children, anogenital warts may indicate sexual abuse but can also result from vertical transmission or autoinoculation, requiring careful evaluation.
### Bowenoid Papulosis
Bowenoid papulosis presents as multifocal pigmented papules on the genitalia. Histologically, it shows full-thickness atypia (Bowen disease/SCC in situ), most commonly associated with HPV 16. It occurs in young adults and typically follows a benign clinical course, but has potential for progression to invasive SCC, especially in immunosuppressed patients.
### Epidermodysplasia Verruciformis (EV)
EV is a rare autosomal recessive genodermatosis caused by EVER1/TMC6 or EVER2/TMC8 mutations, resulting in defective cell-mediated immunity specifically against beta-HPV types. It presents with widespread flat wart-like papules and pityriasis versicolor-like macules from childhood. HPV 5 and 8 are associated with SCC development in sun-exposed areas, carrying a 30 to 60 percent lifetime risk. An acquired EV phenotype can occur in HIV/AIDS and iatrogenic immunosuppression.
## Histopathology
Verruca vulgaris shows papillomatosis, acanthosis, hypergranulosis, koilocytes (enlarged keratinocytes with perinuclear halo and pyknotic, irregular nucleus), parakeratotic columns (church spires), and inward-pointing rete ridges. Flat warts show basket-weave hyperkeratosis, koilocytes in the upper epidermis, and minimal papillomatosis. Condyloma acuminatum shows papillomatosis, acanthosis, and koilocytes; it must be distinguished from condylomata lata (secondary syphilis), which lacks koilocytes and shows a plasma cell-rich infiltrate. Bowen disease (HPV-associated) shows full-thickness keratinocyte atypia with atypical mitoses and a windblown appearance.
## Treatment
### Destructive Methods
**Cryotherapy** is the most common office treatment, using liquid nitrogen at -196 degrees Celsius. An aggressive freeze-thaw-freeze technique is used for plantar warts. Limitations include pain, blistering, potential scarring, and the need for multiple treatments, with efficacy of approximately 50 to 70 percent clearance after multiple sessions. **Electrodesiccation and curettage** is effective for pedunculated warts. **CO2 laser ablation** vaporizes wart tissue, though there is risk of HPV in the laser plume, necessitating a smoke evacuator. **Surgical excision** is reserved for large or refractory warts but carries risk of scarring and recurrence.
### Topical Therapies
**Salicylic acid** (17 to 40 percent) is an evidence-based first-line treatment comparable in efficacy to cryotherapy. It is an over-the-counter keratolytic applied nightly for 12 weeks after paring the wart. **Imiquimod 5% cream** is a TLR7 agonist that stimulates local innate and adaptive immunity, FDA-approved for anogenital warts, applied three times weekly for up to 16 weeks. Local erythema and irritation are expected and correlate with efficacy. **Podophyllotoxin (podofilox) 0.5%** is an antimitotic for anogenital warts applied by the patient. **Sinecatechins 15% ointment** (green tea extract) is FDA-approved for anogenital warts. **5-Fluorouracil (5-FU)** is used topically under occlusion for recalcitrant warts. **Bleomycin intralesional injection** is cytotoxic, painful, and effective for plantar and periungual warts, though there is risk of Raynaud phenomenon and nail damage. **Topical retinoids** (tretinoin) are useful for flat warts on the face. **Cantharidin** is a vesicant applied in-office that causes blister formation to lift the wart; it is painless at application and popular in pediatric dermatology.
### Immunotherapy
**Candida antigen** (intralesional) is injected into a single wart to stimulate an immune response that clears both the injected and distant warts, with a response rate of approximately 50 to 70 percent. **MMR vaccine intralesional** injection follows a similar concept and is used off-label. **Squaric acid dibutylester (SADBE) or diphencyprone (DPCP)** are topical contact sensitizers that induce allergic contact dermatitis at the wart site; the patient is sensitized first, then dilute concentrations are applied weekly. These are used for widespread or recalcitrant warts.
### HPV Vaccination
The **9-valent HPV vaccine (Gardasil 9)** covers HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58. It is recommended for all individuals aged 9 to 26 years, with catch-up vaccination through age 45 via shared clinical decision-making. A 2-dose schedule is used if started before age 15, and a 3-dose schedule if started at 15 or older or in immunocompromised patients. The vaccine is prophylactic (preventing new infection) and not therapeutic for existing infection. It targets the L1 capsid protein and produces neutralizing antibodies, with greater than 90 percent efficacy in preventing HPV 16/18-related cervical, anal, and oropharyngeal cancers and in reducing anogenital wart incidence.
## Warts in Special Populations
### Immunosuppressed Patients
Organ transplant recipients carry a high burden of warts with a 65-fold increased risk of cutaneous SCC. HIV/AIDS patients develop widespread warts with high-grade dysplasia and elevated anal SCC risk. Management requires aggressive treatment, sun protection, HPV vaccination, and regular screening for dysplasia.
### Periungual and Subungual Warts
These are difficult to treat due to their proximity to the nail matrix. Options include cryotherapy, cantharidin, and topical 5-FU under occlusion. Bleomycin should be avoided near the nail matrix due to risk of permanent nail dystrophy. Subungual SCC must be excluded in persistent or atypical periungual lesions.
Clinical photograph panel showing HPV lesion types: (A) verruca vulgaris on the finger with hyperkeratotic papillomatous surface and thrombosed capillaries visible as black dots, (B) plantar wart with disrupted dermatoglyphics and endophytic growth, (C) condylomata acuminata on the genitalia showing soft pink papillomatous papules, (D) flat warts (verruca plana) on the face showing multiple small flesh-colored flat-topped papules. Show diverse skin tones.
Histopathology illustration of verruca vulgaris showing papillomatosis with church-spire configuration, acanthosis, hypergranulosis, inward-bending rete ridges, koilocytes with perinuclear halos in the upper epidermis, and thrombosed capillaries within dermal papillae. Label each feature clearly in H&E-stain style.
HPV treatment algorithm organized by lesion type: common warts (salicylic acid vs. cryotherapy first-line, escalate to immunotherapy or bleomycin), anogenital warts (patient-applied imiquimod/podofilox vs. provider-applied cryotherapy/TCA), and recalcitrant warts (intralesional Candida antigen, SADBE/DPCP contact immunotherapy, or combination approaches). Include vaccination recommendation for prevention.
## Key Clinical Pearls
"Black dots" in warts are thrombosed capillaries, not seeds; paring down the wart to visualize these dots confirms the diagnosis versus callus or corn, which lacks thrombosed vessels. Disruption of dermatoglyphics (skin lines) is the most reliable clinical feature distinguishing a plantar wart from a callus. Condylomata acuminata (HPV 6/11) must be distinguished from condylomata lata (secondary syphilis): condylomata lata are smoother, flatter, and moist, and RPR/VDRL should always be checked in the differential. HPV vaccination is prophylactic, not therapeutic; vaccinating a patient with existing warts does not treat them, but it may prevent acquisition of additional HPV types. In immunosuppressed patients, especially transplant recipients, warts and HPV-related keratoses carry significant risk of progression to SCC, warranting aggressive surveillance and treatment. Intralesional Candida antigen injection can clear distant, untreated warts through immune stimulation, making it an excellent option for patients with numerous warts.
## References
- Lipke MM. An armamentarium of wart treatments. Clin Med Res. 2006;4(4):273-293.
- Doorbar J, Quint W, Banks L, et al. The biology and life-cycle of human papillomaviruses. Vaccine. 2012;30(Suppl 5):F55-F70.
- Meites E, Szilagyi PG, Chesson HW, et al. Human papillomavirus vaccination for adults: updated recommendations of the ACIP. MMWR Morb Mortal Wkly Rep. 2019;68(32):698-702.
- Sterling JC, Gibbs S, Haque Hussain SS, Mohd Mustapa MF, Handfield-Jones SE. British Association of Dermatologists guidelines for the management of cutaneous warts. Br J Dermatol. 2014;171(4):696-712.