Warts are overgrowths of the epidermis (outer layer of the skin) caused by a local infection with human papilloma virus (HPV). One to six months can elapse from the time of infection until warts appear.
The virus is spread primarily by direct skin-to-skin contact from person-to-person, often through a small skin break, abrasion, or trauma. This is why warts are most commonly located on the hands or feet, which frequently sustain minor injuries, and on the genitals, where the virus is transmitted during sexual contact. Warts can also be spread by picking at them and then picking or scratching at some other area.
There are many types of HPV and specific types cause infection on the soles of the feet, hands, legs, or genitals. More information on genital warts can be found here.
On the bottoms of the feet, warts are usually thickened areas of skin where the virus has grown deep into the tissue from weight-bearing activities such as walking and standing. Often a ring of callused skin surrounds the wart and there may be tiny brown-black dots, which are capillaries (small blood vessels) that have broken from the pressure of bearing so much weight.
Since warts are caused by a viral infection, they usually disappear in time with no treatment. This usually takes months to two years, although plantar warts may take longer. Warts disappear after the body has built up sufficient immunity to the virus causing them.
All wart treatments work by damaging the skin cells of the wart to remove skin containing the virus. The effectiveness of treatment also depends on the individual’s immune system and their ability to fight off infections.
Cutting or burning is generally only used in special cases because scarring is more likely than with freezing or chemicals. Cutting or burning usually requires a local anesthetic, as does removal by laser.
Freezing with liquid nitrogen is somewhat painful and creates a blister within a day or so. Do not break the blister: there is less chance for infection if the blister stays intact. Eventually the dead skin sloughs away. Repeated freezing is often necessary after the skin has healed, usually two to four weeks later.
Combination therapies of home treatments and more aggressive clinic treatments are often necessary. For example, plantar warts often require over-the-counter salicylic acid compounds at home and periodic clinic treatments, such as liquid nitrogen. Consult a clinician for the best treatment plan.