Anna Hugo, age 13, of Keen, N.H., for her question:

WHAT CAUSES A HARELIP?

A harelip, more properly called a cleft lip, is a cleft or split through the upper lip. It is sometimes called a hare lip because it resembles a hare's split upper lip. Doctors do not know what causes cleft lip.

Something prevents the lip from growing together before the baby is born.

Cleft lip may be single, that is, only one side of a lip may be cleft. Or both sides of a lip may be open.

Cleft palate, an opening in the roof of the mouth, often occurs with cleft lip. This condition usually causes a speech defect. Cleft palate is congenital, meaning that it is present at birth. It results when the bones of the hard palate fail to join properly as the fetus develops. In most causes, doctors can join the two parts of the palate in an operation.

Sometimes a deformity of the nose also occurs. Doctors can successfully close this type of opening by means of surgical operations.