An Overview of Plantar Warts

What Causes Them and How to Get Rid of Them

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Plantar warts
Marionette/Wikimedia Commons

Plantar warts are those that develop on the bottom of the foot (known as the plantar surface). Caused by the human papillomavirus (HPV), these abnormal but benign growths of skin affect the uppermost layer of skin, known as the epidermis. A plantar wart can spread if you touch, scratch, or pick at it. Some can develop into widespread clusters on one or both feet, only to spontaneously resolve after months or years. Depending on its location, a wart can sometimes press against sensitive tissues and nerve endings, causing pain and discomfort.

While anyone can get a plantar wart, they most typically affect children, teens, and young adults. Some smaller growths can disappear on their own without treatment, and others can often be treated at home with an over-the-counter wart remover. Those that are larger or especially painful may require medical treatment, including cryotherapy or surgical excision.

Causes

All warts are caused by HPV, the same virus associated with genital warts, of which there are more than 100 strains. The type primarily associated with plantar warts is HPV-1. Less common culprits include HPV types 2, 4, 60, and 63.

When infected with HPV, the epidermal cells will begin to multiply rapidly, leading to the formation of a papilloma (wart). Those found are the soles of the feet are commonly referred to as verrucas.

The virus thrives on moist surfaces and can be easily transmitted through tiny breaks in the outermost shell of the epidermis, known as the stratum corneum. After infection, a wart may not develop for several weeks or months. However, once the wart is established, the virus can move from the initial overgrowth to adjacent breaks in the skin.

Not everyone exposed to HPV will develop a wart. People with compromised immune systems, such as those with HIV, are especially vulnerable. Feet that sweat heavily or are regularly exposed to moist surfaces, such as a locker room floor, are also more likely to get warts.

While a plantar wart will tend to resolve over time, around 10 percent of cases will have recurrent episodes. Unlike genital warts, plantar warts are not associated with cancer.

Symptoms

Plantar warts are similar in appearance to corns but are differentiated by their location and structure. While corns are commonly found on the top surfaces of the smaller toes (particularly over a joint), plantar warts tend to develop on the heel or weight-bearing parts of soles. When trimmed back, a plantar wart will have characteristic black dots where enlarged capillaries have hardened. With time, or sometimes even initially, several plantar warts can appear in a grouping.

Plantar warts can often grow inward due to the pressure placed on them when you walk or stand. These warts have grainy, finger-like fibers surrounded by a hardened callus. Inward-growing warts and those located in the skin folds of the toes tend to be the most painful.

Larger plantar warts sometimes split, exposing sensitive tissue and triggering pain and bleeding.

Diagnosis

Plantar warts are typically diagnosed by the appearance of the skin growth. If in doubt, your doctor may trim the growth to see if there are any of the black dots among the fibrous tissues.

If the growth is extensive or atypical, a skin scraping (shave biopsy) may be performed and sent to the lab to check for other similar conditions, such as molluscum contagiosum, squamous cell carcinoma, or a tuberculosis-related complication known as verrucosa cutis.

Treatment

Most plantar warts can be treated at home if they are small and non-intrusive. However, you should always see a doctor if a wart is bleeding, affecting how you walk, is changing in texture or appearance, or is worsening despite treatment. This is especially true if you have diabetes since even a small wart can trigger extreme neuropathic pain or lead to a diabetic foot infection.

Home Remedies

There are numerous over-the-counter (OTC) wart treatments, most of which contain salicylic acid. Some are applied topically with a dropper or swab, while others are applied over the wart with an adhesive bandage. There are even aerosol sprays that can gradually freeze and kill the affected tissue.

Other people rely on the duct tape method, a harmless yet questionable practice in which duct tape is repeatedly applied to a wart to gradually "strip away" the abnormal tissue.

The success of OTC treatments depends largely on the size of the wart and how consistently the treatment is applied. Larger warts tend to be less responsive to OTC treatments.

If using a salicylic acid-based product, it always helps to debride the dead skin cells between treatments with a callus file or pumice stone. Try not to be too aggressive, as this can lead to bleeding, pain, and the formation of a boil or abscess. Be sure to clean the skin thoroughly after debridement, as well as your hands and debridement tools.

Medical Procedures

Based on the appearance of your wart, your doctor may recommend a prescription-strength salicylic formulation to apply at home. If this doesn't help, there are several in-office procedures that may deliver faster and safer results.

Among them:

  • Cryotherapy involves the use of liquid nitrogen to freeze and kill the affected tissue. While generally safe when performed by a doctor, it may require several treatments.
  • Trichloroacetic acid is a stronger acid that needs to be applied by your doctor. As with cryotherapy, it may take several visits to completely remove the wart.
  • Pulsed-dye laser therapy is sometimes used to cauterize (burn) the wart. There is usually significant pain following the procedure. It may also require several treatments performed every three to four weeks.
  • Electrosurgery and curettage involve the use of an electrocautery device and a tool called a curette to scrape off the dead cells. The procedure requires a local anesthetic and tends to cause significant post-operative pain.
  • Surgery is the most direct means of treatment, requiring a local anesthetic and a scalpel to excise the wart. Sutures are usually needed. To avoid infection and the reopening of the wound, you may need to stay off your feet for several days.
  • Cathartan is a blistering agent not approved for use in the United States that is known to cause a blister beneath a wart when injected. This effectively separates the wart from the rest of the skin, causing it to dry up and die.
  • Immunotherapy involves the use of a drug, such as diphencyprone (DCP), that spurs the immune system to eradicate the HPV infection. It is generally reserved for severe cases and may cause an allergic response, including anaphylaxis.

Prevention

Gardasil, Gardasil 9, and Cervarix, the three vaccines used to prevent genital warts, are unable to prevent plantar warts as they target different HPV strains (specifically, types 6, 11, 13, 16, 18, 31, 33, 45, 52, and 58).

To this end, you need to reduce your risk by maintaining good foot hygiene and covering your feet in places where people walk barefoot. If you get professional pedicures, be sure to visit a salon that maintains good cleaning habits (such as sanitizing basins after each use or using tub liners) and consider bringing your own tools.

If you have a plantar wart, change your shoes and socks regularly to avoid the spread of the virus. Always wash and dry your feet thoroughly and use a little talcum powder to help absorb excess moisture and perspiration.

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