Warts are caused by human papillomavirus (HPV) infection. There are over 100 types of HPV.
Warts can develop at any age but are most common among children and least common among older people. People may have one or two warts or hundreds. Warts are contagious. Because prolonged or repeated contact is necessary for the virus to spread, warts are most often spread from one area of the body to another, but they can also spread from one person to another. There usually needs to be a break in the skin for spread to occur, but the break can be extremely small. Sexual contact is often sufficient to spread genital warts.
Most warts are harmless, although they may be quite bothersome. The exceptions are certain types of genital warts that are due to HPV types that can cause cancer of the mouth, throat, or genitals.
Warts are classified by their location on the skin and shape. Some warts grow in clusters (mosaic warts), but others appear as isolated, single growths. Most warts are painless, but some hurt when touched. Warts on the feet can cause pain when standing or walking. Warts may have black dots, particularly if shaved.
Common warts (also called verrucae vulgaris), which almost everyone gets, are firm growths that usually have a rough surface. They are round or irregularly shaped; are light gray, yellow, brown, or gray-black; and are usually less than 1/2 inch (about 1 centimeter) across. Generally, they appear on areas that are frequently injured, such as the knees, face, fingers, and elbows. Common warts may spread to surrounding skin.
Plantar warts develop on the sole of the foot, where they are usually flattened by the pressure of walking and are surrounded by thickened skin.
Palmar warts develop on the palm of the hand.
Plantar and palmar warts tend to be hard and flat, with a rough surface and well-defined boundaries. They are often tender, and plantar warts can be very painful when standing or walking, which puts pressure on them. Warts may appear on the top of the foot or on the toes, where they are usually raised and fleshier. Warts are often gray or brown and have a small black center. Unlike corns and calluses, plantar warts tend to bleed from many tiny spots, like pinpoints, when a doctor shaves or cuts the surface away with a knife.
Periungual warts are thickened, cauliflower-like growths around the nails. The nail may lose its cuticle, and other skin infections (such as paronychia) can develop around the nail. These warts are more common among people who bite their nails or have occupations where the hands are chronically wet such as dishwashers and bartenders.
Flat warts, which are more common among children and young adults, usually appear in groups as smooth, flat-topped, yellow-brown, pink, or flesh-colored spots, most frequently on the face and tops of the hands. They can also develop along scratch marks. The beard area in men and the legs in women are also common locations for flat warts, where they may be spread by shaving. This type of wart typically causes no symptoms but is usually difficult to treat.
Also called venereal warts or condylomata acuminata, genital warts occur on the penis, anus, vulva, vagina, and cervix. They can be flat, smooth, and velvety or irregular, bumpy growths often with the texture of a small cauliflower. Warts around the anus often itch.
Many warts, particularly common warts, disappear on their own within a year or two. Because warts rarely leave a scar when they heal spontaneously, they do not need to be treated unless they cause pain or psychologic distress. Genital warts are treated to prevent spread to a sex partner, but many can be prevented by a vaccine against the human papillomavirus (HPV). All types of warts may return after removal. Plantar warts are the most difficult to cure.
In general, warts can be removed with the following:
Chemicals: Typical chemicals used to treat include salicylic acid, trichloroacetic acid, 5-fluorouracil, cantharidin, tretinoin, and podophyllum resin. Flat warts are often treated with peeling agents such as tretinoin, lactic acid, or salicylic acid. 5-Fluorouracil cream or solution may also be used. Imiquimod, podofilox solution, and sinecatechins can be used for the treatment of genital warts and are sometimes used to treat other warts. Some chemicals can be applied by the person, but others must be applied by a doctor. Most of these chemicals can burn normal skin, so when they are applied at home, directions must be followed carefully. Chemicals usually require multiple applications over several weeks to months. Before applying chemicals to the wart, the wart can first be soaked in hot water to make it easier for the chemicals to penetrate it. The wart is scraped either at home or in the office to remove dead tissue before each treatment.
Freezing (cryotherapy): Freezing is safe when it is done by a trained professional. The area usually does not need to be numbed, but freezing with no numbing may be too painful for children to tolerate. Warts may be frozen with various commercial freezing probes. However, liquid nitrogen sprayed on or applied with a cotton swab is more effective. Cryotherapy is often used for plantar warts, filiform warts, and warts under the fingernails. Multiple treatments at monthly intervals are often required, especially for large warts.
Burning and cutting: These methods are effective but are more painful and usually leave a scar. A laser or electrical current is used to burn warts off. A pulsed dye laser is also effective but, like freezing, usually requires multiple treatments (see Using Lasers to Treat Skin Problems).
Other therapies: An antigen made with the yeast Candida can be injected directly into warts, particularly warts that are difficult to treat. This antigen comes from the yeast. When injected into a wart, it causes an immune response that fights against the virus. The HPV vaccine that protects against 9 strains of HPV may be helpful for children who have warts that are difficult to treat. Warts may also be treated with a combination of the topical antiviral drug cidofovir and a topical form of a drug that stimulates and modifies components of the immune system (an immunotherapy drug).