Plantar warts arise from direct contact with a strain of human papilloma virus (HPV). You may recognize HPV as the virus commonly associated with cervical cancer and genital warts. However, there are more than 100 types of HPV, some of which can cause plantar warts.
Once a plantar wart has developed, it can spread in several ways. Untreated plantar warts can spread on their own into wart clusters or grow to an inch (2.54 centimeters) or more in circumference. A person with plantar warts also can spread them to other areas of the foot by scratching or touching the wart. In addition, contact with any skin or bloodshed from the wart may cause other warts to develop.