Plantar warts are caused by an infection with the human papillomavirus (HPV) in the outer layer of skin on the sole of your feet.

There are more than 100 types of HPV, but only a few types are known to cause warts on your feet. Other types of HPV are more likely to cause warts on other areas of your skin or on mucous membranes.

Transmission of the virus

Each person's immune system responds differently to HPV, so not everyone who comes in contact with the virus develops warts. Even people in the same family react to the virus differently.

The HPV strains that cause plantar warts aren't highly contagious. Therefore, it isn't easily transmitted by direct contact from one person to another. However, the virus does thrive in warm, moist environments — such as shower floors, locker rooms and public swimming areas. Consequently, you may contract the virus by walking barefoot around pools or gyms.

The virus also needs to have a point of entry into the skin:

  • Cracks in dry skin
  • Cuts or scrapes
  • Wet, softened, fragile skin from prolonged water exposure (macerated skin)

Multiple warts

If the virus spreads from the original site of infection, multiple warts may appear. These may include:

  • Several individual warts at different sites on the foot
  • "Kissing warts," a pair of warts that appear where two parts of the foot touch, such as a point of contact between two toes or between a toe and the ball of foot
  • Mosaics, clusters of warts that essentially form a large, single lesion
May. 03, 2011