Plantar warts are benign (noncancerous) growths that occur on the sole (plantar surface), heel, or ball of the foot. Pressure from standing and walking often causes them to grow into deep layers of the skin.
The human papilloma virus (HPV) causes several different types of warts, which are the most common type of skin infection. In some cases, the HPV virus dies within 1 or 2 years, and warts simply disappear. Podiatrists may recommend having plantar warts removed because they often are irritating and painful.
Anyone can contract the virus that causes plantar warts. According to the American Podiatric Medical Association (APMA), plantar warts occur most often in children and young adults between the ages of 12 and 16. Incidence is higher in people who share common bathing areas (e.g., dormitory students, gym members).
Plantar warts can occur when HPV invades the body through tiny cuts or breaks in the skin on the bottom of the feet. The virus often is encountered on contaminated surfaces, such as the tile floors of public locker rooms, showers, and swimming pools. Normally, antibodies in the blood destroy HPV, but in some cases, it takes refuge in the skin and causes plantar warts.
Some people are more prone to the virus that causes plantar warts than other people. Risk factors include repeated HPV exposure (e.g., walking barefoot in public locker rooms and common bathing areas) and having a weakened immune system. In some cases, the virus can be transmitted to the feet from other areas of the body (called remote location seeding).
Plantar warts usually are rough and spongy, and most are gray, brown, or yellow with dark pinpoints (tiny capillaries that supply blood to the wart). Scraping a wart may cause it to bleed.
A plantar wart is similar in structure to an iceberg-the part on the surface of the skin is a small part of the entire anomaly. Often, the portion of the wart under the skin is at least twice as big as the part you can see.
Plantar warts may cause pain on the bottom of the foot. Patients often feel a "lump" on the bottom of the foot when standing, similar to having a stone in the shoe. In many cases, pressure from standing and walking prevents plantar warts from rising above the skin surface.
If left untreated, plantar warts can grow up to 1 inch in circumference and may spread into clusters (called mosaic warts). In severe cases, they cause a change in gait or posture that results in leg or back pain.
Most plantar warts are diagnosed based on their appearance. In some cases, the podiatrist scrapes a sample of skin cells from the wart and sends the sample to a pathologist for microscopic evaluation.
Over-the-counter medications contain chemicals that destroy skin cells (e.g., acid) and may damage healthy tissue surrounding the wart and contribute to spreading. Self-treatment for plantar warts using an over-the-counter preparation is not recommended.
In some cases, podiatrists apply mild acid (e.g., salicylic acid, cantharidin, dichloroacetic acid) topically to treat plantar warts. This treatment, which often requires multiple applications over the course of several weeks, disintegrates viral cells and allows healthy skin cells to replace them.
Laser treatments (e.g., CO2 laser) can be used to treat plantar warts. Laser treatment is performed in a podiatrist's office or an outpatient surgery facility using local anesthesia. Lasers produce little scarring and are effective in most cases.
Cryotherapy involves freezing warts with a very cold solution (e.g., sodium nitride) that destroys the virus and causes the wart to turn black and fall off within a few days. This treatment is ineffective in some cases when the solution does not penetrate far enough to completely destroy the virus.
Surgical removal (called curettage) is a common procedure performed in a podiatrist's office under local anesthesia. Generally, this procedure is used to remove isolated warts, areas not greater than 1–2 cm, or several small warts in a limited area (mosaic patches). Surgical curettage can be combined with other treatments, as necessary.
According to the American Podiatric Medical Association (APMA), the following may help to prevent plantar warts:
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