Are there risks factors for not treating Plantar Warts? What are Plantar Warts? Warts are caused by an infection of the skin by human papillomavirus (HPV), which is the most common viral infection of the skin. Plantar warts grow on the plantar surface or the sole of the foot. They can be found anywhere in this area, but tend to produce symptoms in areas of pressure and/or friction. The virus that causes warts, the human papillomavirus, infects only the superficial layer of skin, producing a thickened callus-like growth that, if located in an areas subjected to pressure, can become quite tender. Although warts characteristically resolve spontaneously, it is sometimes necessary to treat painful plantar warts. The incubation period (the period of time between infection and the production of the visible skin lesion) is not known but estimates vary from months to years. There are at least 120 different types of (HPV), and certain types tend to infect specific anatomical areas, like the plantar surface of the foot. HPV infections are ubiquitous infections, with least one-half of adults infected during their lifetime.