Flat Warts: Symptoms, Types, Causes and Treatment

Flat warts—also known as verruca plana—are a unique form of wart that can be both a cosmetic concern and an indicator of underlying health. Unlike common warts, flat warts are subtle, often blending into the skin, and they frequently appear in clusters, especially on the face, hands, and shins. Understanding their symptoms, types, causes, and modern treatments can empower individuals and caregivers to better manage and treat this condition.

Symptoms of Flat Warts

Flat warts are often mistaken for other skin conditions due to their subtle appearance. Recognizing the hallmark symptoms is essential for early identification and effective treatment. They most frequently affect children and young adults but can appear at any age. Flat warts tend to spread via self-inoculation—often following scratching or shaving—and may cause distress due to their visibility, especially on the face.

Appearance	Location	Spread	Source(s)
Smooth, flat, flesh- or brown-colored papules	Face, hands, shins, trunk	Linear or clustered arrangement (due to self-inoculation)	1, 5, 6
Slightly elevated, small (1–5 mm)	Face, dorsal hands, forearms	May increase in number over time	5, 6
Minimal symptoms (rarely painful or itchy)	Around trauma sites (scratches, shaved skin)	More common in children, teens, immunocompromised	3, 5, 6

Table 1: Key Symptoms

Appearance and Texture

Flat warts are characteristically small—typically 1 to 5 mm in diameter—and have a smooth, slightly raised surface. Their coloration can range from skin-colored to light brown, making them blend with the surrounding skin. Because of their flatness and subtle pigmentation, they are often overlooked at first glance 5, 6.

Common Locations

Flat warts most often develop on the face, especially the forehead and cheeks, and on the backs of the hands and forearms. In children, they may also appear on the legs or trunk. Self-inoculation is common, resulting in linear arrangements or clusters, particularly in areas prone to minor trauma, such as from shaving or scratching 5, 6.

Spread and Risk Factors

Flat warts are typically asymptomatic, causing little to no discomfort. However, their tendency to multiply, especially in lines, can be distressing. They occur more frequently in younger people and individuals with compromised immune systems, such as those with HIV or on immunosuppressive medications 3, 6.

Types of Flat Warts

While all flat warts share certain clinical features, several types can be distinguished based on their viral cause and patient context. Recognizing the diversity of flat wart types is vital for proper diagnosis and management, especially in complex or atypical presentations.

Type/Variant	Typical Host	Associated HPV Types	Source(s)
Common flat (juvenile) warts	Children, young adults	HPV 3, 10, 28, 29, 41, 94, 95	1, 5, 6
Flat warts in immunocompromised	HIV+, immunodeficiency	HPV 3, 5, 28, 29, 95, 94	3, 4, 6
Cervical flat warts	Adult women	HPV 16 (oncogenic), others	2
Epidermodysplasia verruciformis (EV)	Genetic disorder	EV-type HPVs (e.g., 5, 94)	4

Table 2: Flat Wart Types and Variants

Common Flat (Juvenile) Warts

The most familiar type, these warts primarily affect children and teens. They are linked to HPV types 3 and 10, though types 28, 29, 41, 94, and 95 are also implicated in some populations 1, 5, 6. Typically, these warts are small, smooth, and appear in clusters on the face and hands.

Flat Warts in Immunocompromised Patients

Individuals with weakened immune systems—including those with HIV, those undergoing immunosuppressive therapy, or with rare genetic disorders—can develop widespread or atypical flat warts. HPV type 5 has been noted in such cases, which may resemble tinea versicolor or be unusually extensive 3, 4. These warts may also be more resistant to standard therapies.

Cervical Flat Warts

On mucosal sites like the cervix, flat warts may be caused by oncogenic HPV types, notably HPV 16. These lesions can show atypical cellular changes and, in rare cases, may serve as precursors to cervical cancer 2. Such warts are usually detected during gynecological exams, rather than visually.

Epidermodysplasia Verruciformis (EV)-Associated Flat Warts

EV is a rare genetic disorder characterized by susceptibility to certain HPVs, including types 5 and 94. Patients present with a wide range of flat wart–like lesions and have a higher risk for skin cancer. These cases highlight the genetic interplay in wart formation and persistence 4.

Causes of Flat Warts

Understanding what causes flat warts—especially the viral culprits and host factors—can help prevent their spread and recurrence. At their core, flat warts are an infectious disease, but their development is influenced by immunity and, in rare cases, genetics.

Cause	Detail/HPV Types	Risk Factors	Source(s)
Human papillomavirus	Types 3, 10, 28, 29, 41, 94, 95, 5, 16	Children, teens, immunocompromised, genetic disorders	1, 3, 4, 5, 6
Immunosuppression	HIV, immunosuppressive drugs, cancer	Wider, treatment-resistant warts	3, 4, 6
Genetic predisposition	Epidermodysplasia verruciformis	Defects in keratinocyte/T-cell immunity	4
Self-inoculation	Spread via scratching/shaving	Linear/clustered lesions	5

Table 3: Flat Wart Causes and Risk Factors

Human Papillomavirus (HPV) Infection

Flat warts are caused by infection with specific types of HPV—a group of DNA viruses that infect skin and mucous membranes. The most common HPV types in flat warts are 3, 10, 28, and 41, though other types (including 29, 94, 95, and 5) are sometimes detected, especially in atypical cases 1, 5, 6. In cervical flat warts, high-risk types like HPV 16 are implicated 2.

Host Immunity

The immune system plays a central role in controlling HPV infections. Immunosuppressed individuals—such as those with HIV, those on steroids or chemotherapy, or with certain genetic conditions—are more susceptible to widespread, persistent, or treatment-resistant flat warts 3, 4, 6. These cases often involve uncommon HPV types and may present atypically.

Genetic Factors

Rare genetic disorders like epidermodysplasia verruciformis (EV) dramatically increase susceptibility to EV-associated HPVs, leading to extensive flat wart–like lesions and increased skin cancer risk 4. EV results from inherited defects in skin or immune cell function, highlighting the host–virus interaction in wart formation.

Transmission and Spread

Flat warts are usually spread by direct skin-to-skin contact or via contaminated objects. Self-inoculation—transferring the virus from one area of the body to another by scratching or shaving—is a common reason for the characteristic linear or grouped pattern of flat warts 5. Children and teens are especially prone due to frequent minor skin trauma.

Treatment of Flat Warts

Flat warts can be stubborn, especially in adults or immunocompromised patients. While some warts resolve spontaneously, many require targeted treatment for cosmetic reasons or due to persistence. The choice of therapy depends on wart location, number, patient preference, and any underlying health conditions.

Treatment	Description	Effectiveness/Safety	Source(s)
Cryotherapy	Liquid nitrogen freezing	Common, may cause discomfort	5, 7
Topical retinoids	Vitamin A-based creams	Useful for facial warts	5, 7
Oral isotretinoin	Systemic retinoid	Very effective for recalcitrant cases	7
Topical salicylic acid	Keratolytic agent	Safe, slow-acting	5
Imiquimod	Immune response modifier	Variable results, especially in immunocompromised	6
Cantharidin	Causes blistering, wart destruction	Highly effective for facial flat warts	8
Laser/light therapies	PDL, YAG, PDT, infrared	Fast results, good cosmetic outcome	9, 10, 11
Photodynamic therapy	ALA-based, conventional or daylight	Effective, especially in children	11
Local hyperthermia	Heat application	Effective for extensive warts	5

Table 4: Flat Wart Treatments

Standard Topical and Physical Therapies

• Cryotherapy: Freezing with liquid nitrogen is a mainstay treatment, though it can be uncomfortable and may cause pigment changes, especially on the face 5.
• Topical retinoids: Creams like tretinoin disrupt wart cell growth and are favored for facial warts due to their minimal scarring risk 5.
• Salicylic acid: This over-the-counter keratolytic is safe but may require weeks to months of consistent use 5.

Systemic Treatments

• Oral isotretinoin: Highly effective for recalcitrant facial flat warts, with all treated patients in one study achieving complete clearance. Side effects are typically manageable (e.g., dry lips) 7.

Immunomodulatory and Chemodestructive Agents

• Imiquimod: Stimulates local immune response, but results can vary, especially in immunocompromised patients 6.
• Cantharidin: A topical blistering agent applied in the clinic, shown to clear facial flat warts in all patients in one study, with only mild skin reactions noted 8.

Laser and Light-Based Therapies

• Pulsed dye laser (PDL): Demonstrated rapid, cosmetically excellent results for facial flat warts, with low recurrence 9.
• Other lasers and photodynamic therapy (PDT): Systematic reviews highlight the promise of YAG laser, infrared coagulation, and PDT (using aminolevulinic acid, ALA) 10, with both conventional and daylight PDT found effective and well tolerated in children 11.

Other Modalities

• Local hyperthermia: Controlled heat application has been reported to successfully treat extensive flat warts, even those resistant to other methods 5.

Considerations for Special Populations

• Immunocompromised patients: May require more aggressive or prolonged therapy, and warts may be more resistant to standard treatments 3, 4, 6.
• Children: PDT, especially daylight-based, is well tolerated and yields excellent cosmetic results 11.

Conclusion

Flat warts are a common and sometimes persistent skin problem, especially in children and those with weakened immunity. Their subtle appearance can delay diagnosis, but a growing understanding of their causes and the diversity of treatment methods now offers hope for effective management.

Key Takeaways:

• Flat warts are smooth, flat-topped papules, most often on the face, hands, and shins.
• They are caused by infection with specific HPV types, especially HPV 3 and 10, but many variants exist.
• Host immunity and genetics can influence susceptibility, severity, and treatment response.
• Treatments range from topical agents and cryotherapy to systemic retinoids, immunotherapies, and advanced laser or photodynamic therapies.
• Most cases can be managed effectively, but recalcitrant or atypical warts may require specialized care.

With careful diagnosis and tailored therapy, most individuals with flat warts can achieve excellent cosmetic and clinical outcomes.