Tony Klippel, age 11, of Gary, Ind., for his question:

WHAT CAUSES BIRTHMARKS?

A.discoloration or blemish of the skin that is determined before a baby is born is called a birthmark or nevus. We don't know what causes it, although we do know there is nothing that can be done to prevent it from developing. It's part of the mystery of life.

Some people say that a birthmark may be related to something that happens to the mother before her baby was born. We know this isn't so, just as the mark is not related to anything that happens during birth. Some birthmarks develop after birth, but the skin defect has been there since the time the skin was formed during prenatal life.

Birthmarks may be large or small. Some people have them while others do not.