Plantar warts are caused by an infection with the human papillomavirus (HPV) in the outer layer of skin on the soles of your feet. There are more than 100 types of HPV, but only a few types are known to cause warts on your feet.
The viruses 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, such as:
- Cracks in dry skin
- Cuts or scrapes
- Wet, softened, fragile skin from prolonged water exposure
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