DEAR DR. DONOHUE: My legs, ankles and feet get really swollen, and I mean really. During the day, if I slip my shoes off, I can’t get them back on. What can I do to take down the swelling? I’m not on any medicine, and my health is good. I haven’t seen a doctor in quite a while. — M.M. ANSWER: The swelling you have is called edema. You need some background information to understand why it happens. Fluid constantly (and normally) leaks out of the circulation to bathe all body cells, tissues and organs. It returns to the circulation by way of lymphatics, vessels that act like suction hoses to vacuum up lymph fluid and return it to the circulation. Many things can cause an excessive leakage of this fluid. One big cause is congestive heart failure. The failing heart can’t pump much blood with each beat. Blood backs up into the circulation, and fluid leaks out to swell the legs, ankles and feet. Medicines often can strengthen the heart, and other medicines can get rid of too much fluid. Liver and kidney diseases also bring fluid retention and edema formation. A clot in a leg vein can swell the leg, ankle and foot, but this just about always happens to only one leg. Salt retention causes the body to hold onto fluid, and the circulation is overwhelmed by it. That extra fluid leaks out and brings on edema. One somewhat innocuous cause is sitting too long or standing in one place too long. Gravity pulls fluid from the circulation.