Infection: Warts

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Infection: Warts

Causes and Symptoms
The Future
For more information


Warts are small benign (noncancerous) growths of tissue on the surface of the skin caused by the human papillomavirus (HPV). Most are skin-colored but some are darker than the surrounding skin. Dermatologists (doctors who specialize in treating skin disorders) classify warts into four main types according to their location on the body:

  • Common warts: Usually found on the fingers, fingernails, and backs of the hands.
  • Plantar warts: Found on the soles of the feet. Plantar warts that form in groups are sometimes called mosaic warts.
  • Flat warts: Located on the face or (in men) the beard area.
  • Genital warts: Found on the external genital areas or around the anus.


Warts are small growths on the surface of the skin that result from one or more strains of human papillomavirus infecting the skin through small breaks in the outer surface of the skin. The virus can be transmitted from one person to another; genital warts are highly contagious, whereas the risk of getting common, plantar, or flat warts directly from another person is relatively small.

The external appearance of warts varies somewhat according to location. Common warts are usually the same color as the surrounding skin and may occur around the edges of the nails where the person has chewed on or cut off a hangnail. The blood vessels inside the wart may look like black dots or seeds.

Plantar warts are usually flat because of the pressure of walking or running. They usually are grayish-yellow in color and may also have black dots inside them like common warts. Plantar warts typically form on parts of the foot that are under pressure from shoes, like the heel or ball of the foot. These warts can be painful as well as unattractive.

Flat warts are smaller (about one-quarter inch[0.64 centimeter]) and smoother than common warts. They are most likely to occur on parts of the body where the skin may be cut or broken by shaving, like the face in men or the legs in women.

Genital warts are a sexually transmitted infection. They usually appear in clusters, which may be very small or may develop into large masses of tissue around the anus or the exterior genitals. In women, genital warts can grow inside the vagina as well as outside it. Genital warts are not cancerous.


Warts are widespread in the general American population. Between 7 and 10 percent of people develop plantar warts. Flat warts and plantar warts are more common in children and teenagers than adults. Women are slightly more likely than men to develop plantar warts.

Causes and Symptoms

Warts are caused by infection with the human papillomavirus. There are over 130 strains of this virus that have been identified as of the early 2000s. The virus thrives in warm, moist environments like shower stalls or locker rooms, which is why it can be transmitted indirectly from one

person to another. It takes between one and eight months for a wart to appear after the virus has entered a person's body through a break in the skin.

Some people are more susceptible to warts than others, most likely because of genetic factors. No specific genes, however, have been associated with warts.

The symptoms of warts have already been described. Plantar warts are the only type of wart that are usually painful.


Warts can usually be diagnosed by looking at them. When in doubt, a person should consult their doctor to make sure the growth of tissue is really a wart. The doctor can diagnose a wart by scraping off some of the tissue and sending the sample to a laboratory for analysis. Another technique, which involves injecting a local anesthetic beforehand, is called a punch biopsy. The doctor takes an instrument called a punch and removes a disk-shaped piece of tissue to send to the laboratory.


Common or flat warts do not always need treatment. About 30 percent of warts will disappear by themselves within six months. Most will disappear without any treatment within three years. Since warts are not cancerous, most people choose to treat them either because they are unattractive or because (like plantar warts) they cause discomfort when walking.

When to Call the Doctor about Warts

A person should see their doctor about warts if they notice any of the following:

  • The wart is bleeding heavily or has such signs of infection as red streaks, pus, or a discharge.
  • The patient develops a fever of 101°F(38.3°C) or higher.
  • The wart is painful.
  • The wart is in the anal or genital area.
  • The wart has changed its color or overall appearance.
  • The patient has diabetes, HIV infection, or an immune system weakened by cancer chemotherapy.

People can treat common or flat warts at home in several different ways:

  • Using over-the-counter preparations containing salicylic acid. It comes in two forms, a liquid to be painted directly on the wart or a sticky plaster to be cut and pasted on the wart. Salicylic acid should not be applied to normal tissue surrounding the wart. It can take as long as twelve weeks to remove warts by this method.
  • Covering the wart with adhesive tape or duct tape. This technique works because it forms an airtight environment. The tape is left on for a week, then removed, and the wart is scraped with an emery board or pumice stone.
  • If home treatment does not work, it is best to see the doctor, because the skin growth may be a mole or something other than a wart.
  • Genital warts should never be treated with home remedies. These warts require professional medical care.

Doctors can treat warts with various medical or surgical techniques:

  • Cryotherapy. Cryotherapy uses liquid nitrogen to freeze the warts. The dead tissue in the wart falls away from the skin beneath in about a week.
  • Imiquimod. Imiquimod is a topical cream that gets rid of warts by stimulating the body's immune system to fight the virus that causes the warts.
  • Cantharidin. Cantharidin is a substance derived from blister beetles. It is a liquid that the doctor applies directly to the skin and covers with a bandage. The cantharidin causes the skin to blister, which lifts the wart from the skin surface and allows the doctor to remove the wart surgically.
  • Surgery. The doctor can remove the wart by treating it with an electric needle, then scraping the tissue with a sharp instrument called a curette. Lasers can also be used to remove warts. Both types of surgery can leave scars, however, and are usually used only for warts that have not responded to other types of treatment.


As has already been mentioned, about a third of warts will go away without treatment in a few months. Warts often regrow after the skin has healed because the virus that causes them remains in the body; plantar warts are especially likely to reappear. Salicylic acid is about 75 percent effective in removing warts even though it is a slow method.


People can lower their risk of getting or spreading warts by:

  • Avoiding cutting, shaving, brushing, or picking at warts. These actions can spread the virus that causes warts into other areas of nearby skin.
  • Avoiding biting their fingernails. The virus that causes common warts often enters the skin of the hands through bitten areas of skin.
  • Wearing shower shoes in locker rooms or public showers.
  • Washing the hands carefully after touching a wart.
  • Keeping the hands and feet as dry as possible, since the HPV virus grows and spreads in warm, moist environments.
  • Avoiding sexual contact with anyone known to have genital warts. There is also a vaccine for women that prevents infection with the strains of HPV that cause cervical cancer.

The Future

Common, flat, and plantar warts are widespread minor health problems that are likely to continue to affect children as well as adults. It is possible that researchers may eventually identify specific genes that make some people more susceptible to getting warts.

SEE ALSO HPV infection


Benign: Not cancerous.

Cryotherapy: The use of liquid nitrogen or other forms of extreme cold to treat a skin disorder.

Plantar: Located on or referring to the sole of the foot.

Topical: Referring to a type of medication applied directly to the skin or outside of the body.

Verruca (plural, verrucae): The medical term for a wart.

For more information


Kinch, Michael P. Warts. New York: Franklin Watts, 2000.

Royston, Angela. Warts. Chicago, IL: Heinemann Library, 2002.


O'Neil, John. “Remedies: A Clear Winner in Curing Warts.” New York Times, September 3, 2002. Available online at (accessed June 28, 2008).

O'Neil, John. “Treatments: For Warts, the Duct Tape Cure.” New York Times, October 15, 2002. Available online at (accessed June 28, 2008).


American Academy of Dermatology (AAD). Warts. Available online at (accessed June 28, 2008).

American Academy of Family Physicians (AAFP). Warts. Available online at (updated May 2008; accessed June 28, 2008).

Mayo Clinic. Common Warts. Available online at (updated February 16, 2008; accessed June 28, 2008).

TeensHealth. Warts. Available online at (updated November 2007; accessed June 28, 2008).