Wart Causes, Symptoms, and Treatments

illustration of a wart
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Warts are actually benign (non-cancerous) tumors of the epidermis (the top layer of the skin) caused by a virus. The virus responsible is the human papillomavirus (HPV), a double-stranded DNA virus. The virus resides in the bottom layer of the epidermis and replicates in a way in which the appearance is very similar to normal-looking skin.

Different sub-types of HPV cause different types of warts. Some human papillomavirus subtypes also cause cervical cancer and other more obscure types of wart-related cancers.

The Appearance of Warts

Warts normally grow out of the skin in cylindrical columns. These columns do not fuse when the wart grows on thinner skin, such as the face. On thicker skin, however, the columns fuse and are packed tightly together giving the surface the typical mosaic pattern.

Black dots can sometimes be seen in a wart. These are actually blood vessels that have grown rapidly and irregularly into the wart and have clotted off or thrombosed. They are not "seeds" of the wart as one myth has stated.

The Wart Root Myth

Contrary to popular belief, warts do not have "roots." They only grow in the top layer of skin, the epidermis. When they grow, they can displace the second layer of skin, the dermis, but they do not grow into the dermis. The underside of a wart is actually smooth.

Who Gets Warts?

Warts can occur in people of all ages but occur most commonly in children and young adults. They spread by direct contact, simply by touching the wart. Warts normally resolve spontaneously but the time it takes for this resolution is variable.

Most warts resolve within weeks or months even without treatment, but some may take many years or decades. It appears that a person's susceptibility to warts and the time it takes for them to go away is related to the individual's immune system. People who have immune-related diseases such as AIDS and lymphoma—or those who are receiving chemotherapy—tend to have more warts that last longer.

Treatments for Warts

As noted above, warts often resolve on their own in time. Yet most people do not wish to wait for this to happen, either because the warts are uncomfortable or for cosmetic reasons. Many warts can be treated with simple over-the-counter remedies, but for warts that are resistant to these therapies, there are other effective treatments. Let's take a look at some of the different options.

Salicylic Acid for Warts: Salicylic acid is a very common and effective over-the-counter treatment but requires consistent application every day. The best way to use salicylic acid is to first pare the wart with a blade, pumice stone, emery board or small scrub brush. Soaking the wart in warm water will aid in the absorption of the medicine.

Salicylic acid is applied to the wart and allowed to dry. The normal surrounding skin may be protected with petroleum jelly, and you may wish to outline the wart with this prior to treatment to avoid treating normal skin surrounding the wart.

Occluding the treated wart with a band-aid or piece of tape also improves the absorption of the medicine, and can decrease the chance the medicine will get on normal skin. Make sure to wash your hands after application and avoid contact of the treated area (for example, if on your fingers) with your eyes.

Salicylic acid applications should be repeated daily ideally, around shower or bath time. Salicylic acid can be found in several forms, including a thick oil or incorporated into an adhesive plaster form.

Other Medications for Warts: Other medicines that may be applied to warts or injected into them include lactic acid, trichloroacetic acid (TCA), formalin, glutaraldehyde, cantharidin, podophyllin, Retin-A, and bleomycin. These treatments should be supervised by a health care provider.

Duct Tape Treatment for Warts: An increasingly used home remedy for warts is duct tape. To do this, duct tape (any color) is applied to the wart and kept in place for six days. After this period of time, you should soak the wart and pare it down with an emery board or file to remove the top layer. After waiting 24 hours, duct tape can again be applied for another six days. This may need to be repeated depending on the size and location of the wart.

Studies have shown mixed results with duct tape, but it is a home remedy with few side effects.

Freezing Warts: Cryotherapy (freezing) is another effective treatment for warts. A healthcare provider applies liquid nitrogen—as a spray or on a cotton swab—to the wart. This freezes and kills the affected cells. The connective tissue is not destroyed; therefore, the lesion usually heals without significant scarring.

The human papillomavirus is not killed by cryotherapy and is released into the surrounding tissue allowing the immune system to kill it. A blister typically forms on the site treated, crusts over, and falls off. Since blisters are painful to walk on, cryotherapy is not the first choice for warts on the bottom of the foot (plantar warts).

Heat Therapy, Surgery, and Other Options for Resistant Warts: Some warts do not seem to respond to repeated treatments with topical medicines, cryotherapy, or even duct tape. In this case, your doctor may recommend cautery (freezing) or surgically removing the wart. The area beneath the wart is usually numbed with lidocaine before surgery is done. The combination of Aldara (imiquimod 5 percent) plus duct tape may also be helpful with recalcitrant warts.

Finally, further treatments such as pulsed dye laser, photodynamic treatment, or injecting Candida antigen, other antigens, dinitrochlorobenzene, or vitamin D directly into the wart have all been tried.

In one study with resistant warts, vitamin D had an almost a 90 percent complete success rate for recalcitrant warts.

The Bottom Line

Warts are very common, especially in children and young adults. They are caused by direct contact with a virus. In time, most warts will go away on their own, yet they can be annoying and unsightly when left untreated.

Many options are available to get rid of warts, from over-the-counter topical preparations to freezing or burning in the clinic.

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