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.
Incidence and Prevalence
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).
Cause and Risk Factors
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.
Signs and Symptoms
Plantar warts usually are rough and spongy, and most are gray or brown 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. 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.
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 debridement) usually is not recommended to treat plantar warts because it can cause painful scarring. Generally, this procedure is used to remove several small warts in a limited area. Debridement is performed using anesthesia and can be used with acid to destroy the virus and prevent the warts from regrowing.
According to the American Podiatric Medical Association (APMA), the following may help to prevent plantar warts:
Avoid walking barefoot whenever possible.
Change shoes and socks daily.
Keep feet clean and dry.
Check children's feet periodically.
Avoid direct contact with warts on other persons or on other parts of the body.
Do not ignore growths on, or changes in, your skin.