What causes plantar warts?

Causes of Plantar Warts

Plantar warts are caused by infection of keratinocytes in the epidermis by human papillomavirus (HPV), primarily types 1,2,4,27, or 57, which enters through small breaks in the skin and causes epidermal thickening and hyperkeratinization. 1

Transmission and Risk Factors

• HPV can spread from one individual to another through direct skin-to-skin contact or via the environment (indirect contact) 1

• The virus can persist outside the body for extended periods - while the exact duration for HPV is unknown, related bovine papillomavirus is believed to retain infectivity for months or possibly years 1

• Common transmission routes include:

  • Walking barefoot in communal areas such as swimming pools, locker rooms, and showers 1
  • Direct contact with infected individuals 1
  • Sharing of equipment in sports settings 1

• A study of adolescents found that 27% of those who used communal showers regularly had plantar warts compared to only 1.25% of those who only used locker rooms 1

Pathophysiology

• After infection at the basal layer of the epidermis, the virus causes clonal proliferation of keratinocytes 1
• This proliferation eventually results in a visible wart after weeks or months of incubation 1
• The virus stimulates excessive keratin production, leading to the characteristic thickened appearance 1
• Plantar warts specifically affect the soles of the feet and tend to be flatter than common warts due to pressure from walking 2
• The virus can shed from existing warts, potentially infecting other sites on the foot or spreading to other people 3

Epidemiology

• Warts are common worldwide, affecting approximately 5-30% of children and young adults 1
• Plantar warts specifically affect up to 33% of children and 3.5% of adults 4
• Infection can occur at any age but is more common in childhood 1
• Individuals with compromised immune systems are at higher risk for developing persistent or extensive warts 1

Natural History

• Warts can persist for years with little or no sign of inflammation 1
• Spontaneous clearance occurs in approximately:
  • 30% of cases within 6 months
  • 60% of cases within 2 years 1
• In children, clearance tends to occur more quickly, with about half clearing at 1 year and two-thirds by 2 years 1
• In adults, warts can be much slower to clear, with persistence for 5-10 years not uncommon 1

Clinical Implications

• Plantar warts can be painful when pressure is applied, affecting mobility and quality of life 2, 5
• They are often resistant to treatment, requiring multiple therapeutic approaches 4, 5
• Distinguishing plantar warts from other foot lesions (corns, calluses) is important for proper management 1
  • Paring down a wart will often result in pinpoint bleeding as capillary loops of elongated dermal papillae are exposed, which is a distinguishing feature 1

Understanding the viral etiology and transmission patterns of plantar warts is essential for both prevention and effective treatment strategies. Avoiding barefoot walking in communal areas and maintaining good foot hygiene are important preventive measures.