Mitzi Culler, age 13, of Kernersville, N.C., for her question:

What causes warts?

At one time, it was thought that people got warts by touching toads. After all, the toad does have warty bumps on his clammy skin and it seemed logical to suppose that they are infectious. But modern researchers disagree with this old theory. They tell us that a hard, bumpy little wart is caused by a virus that enters the surface layer of the skin. There it thrives and multiplies, causing a wad of tough, dead skin cells. Usually a smallish wart lingers a few weeks and gradually disappears. But if the bump is scratched or torn apart, viruses may escape and infect other parts of the skin. So it is wise to stick a bandage over it to protect yourself and others. If the wart keeps growing or lingers too long, it is a good idea to have a doctor take a look at it. He can treat it to dry up and disappear in a few days.