Janet Triffin, age 13, of Baltimore, Md., for her question:

WHY DO SOME PEOPLE HAVE VARICOSE VEINS?

Varicose veins are swollen veins. Some people have them because the walls of their veins are weak from the time they are born. With other people, disease or injury can cause the problem.

Veins of the legs often become varicose if the person must stand a great deal. If the vein walls tend to be weak, the pressure of blood moving toward the heart could be slowed.

In the veins are valves. When the valves can no longer prevent backflow off a column of blood, abnormal pressures dilate the vein system, causing stagnation and pooling of blood.

Heredity seems to be an important factor in varicose veins. Most women and men who suffer from the problem will have had parents or grandparents who have had varicose veins.

What should you do about them? Exercise is beneficial, especially walking and swimming where the muscles of the legs will help to push the blood up the veins. Sit with legs elevated from time to time. On long auto trips, get out and walk a bit every hour. And do not cross the legs at the knees while sitting, since it can hamper the flow of blood.