Dear Dr. Jeff: Are warts contagious? ?T.P.

Dear T.P.: Warts are caused by an infection of skin cells by human papillomavirus (HPV). They are very common, second only to acne among dermatological problems and affect at least three out of four of us at some point in our lives. There are more than 70 subtypes of HPV, and all of them incorporate their DNA into infected cells, possibly remaining in our bodies for life. During times of physical or emotional stress, when our immune systems are weakened, viral proliferation can start up and warts appear.

Warts are classified according to location. Different viral subtypes have marked predilections for different types of skin, and thus different parts of the body. Common, elevated warts typically appear on the hands and are caused by eight different subtypes. Other HPV subtypes cause flat warts (usually appearing on the face and legs), genital warts (found in the anogenital areas), and callus-covered plantar warts (on the soles of our feet).

Humans are the only known reservoir of HPV. No other animals, including toads, are known to carry or transmit the virus. Direct person-to-person transmission of non-genital warts is relatively inefficient. Transmission of HPV occurs primarily through direct contact with infected skin cells. The virus presumably enters through small breaks in the skin. HPV is quite hardy and can survive for considerable periods of time on fomites (inanimate objects such as towels), or in infected skin cells that are sloughed off and lay about on the floor. Plantar warts, for instance, are thought to be contracted most often in this way, around swimming pools and in communal showers.

The incubation period after inoculation with HPV is unknown, but is probably no less than several months. The latency period for genital warts may be particularly long. Auto-inoculation of HPV from one part of the body to another can also occur.

Most non-genital warts disappear on their own without treatment (up to 80 percent within two years). Warts can be bothersome, though, and two years can come to feel like a long time! They can bleed if bumped, and they can also seem embarrassing. Treatment of warts likely decreases the chances that they'll spread to other areas of your body or to other people.

Common and plantar warts are often effectively treated with over-the-counter remedies. Perhaps the most effective therazpy involves covering warts with tiny bandages made from duct tape. It turns out that some component of duct tape adhesive is viricidal. The efficacy of duct tape was clearly demonstrated in a study published a few years ago in the New England Journal of Medicine!

Flat warts, facial warts, and genital and oral warts are usually treated in a medical office, using a variety of "ablative" and "medical" therapies. Ablative treatments include surgical excision, destruction by electrodessication, laser or liquid nitrogen, and chemical "peeling." Topical medical treatments include daily applications of cytotoxic, antiviral, or immunotherapy agents, in the hope of inducing a controlled, localized allergic or immunologic reaction to the infected cells.

Innumerable "alternative" remedies for warts have been tried over the ages, with varying degrees of success. With the important exception of anogenital warts (which can be mutagenic), there may not be a compelling reason to rush in for "high tech" medical treatment.

As always, though, all of us at the health center are happy to see you and discuss any questions or concerns you might have. We have a thermos tank filled with liquid nitrogen, and we're also happy to prescribe immunotherapy creams.

Be well! And wear your flip-flops in showers and locker-rooms!

Jeff Benson, M.D.
Dudley Coe Health Center