Question: My granddaughter has quite a few warts on her skin. What is the cause - and the cure?

Answer: Warts are caused by a human virus, not by kissing (or even holding) a frog. The specific virus that causes warts is the human papilloma virus (HPV), of which there are at least 60 types. As you know, warts can grow on all parts of the body, including the skin, genital area and rectal area. The latter two are transmitted through sexual contact.

Although it is known that we contract HPV through direct contact with a wart, we are not sure why some people get warts and others don't. We do know that cracked or broken skin allows the virus to penetrate more easily, which may explain why children and adults who bite their fingernails or pick at hangnails and scabs seem to get more warts. And our own immune system plays a role in how likely we are to get warts, just as it is a factor in why some people get more colds than others.

Treatment of warts on the skin depends upon their location and the age of the patient. For common warts on the skin, chemical acid like salicylic acid can be applied many times over several weeks to gradually destroy the tissue. Cantharidin can also be applied to chemically destroy the wart. The downside of chemical destruction is that it tends to destroy healthy surrounding skin. Controlled freezing is my preferred method of treatment of warts.

For treatment-resistant warts, electrosurgery and laser are great options. Warts on the feet are treated in much the same way, but they're a bit harder to remove since the bulk of the wart is below the skin's surface.

I've heard plenty of stories of folk remedies, from coal tar to onions, axle grease and garlic. Since warts, especially in children, may spontaneously disappear over time, however, it's hard to say whether they made a difference.