Swelling of the feet, ankles and legs, also called edema, is often caused by an abnormal build-up of fluids in ankle and leg tissues. 

Painless swelling of the feet and ankles is a common problem, particularly in older people. It may affect both legs and may include the calves or even the thighs. Because of the effect of gravity, swelling is particularly noticeable in the lower legs. 

When squeezed, the fluid will move out of the affected area and may leave a deep impression for a few moments. Swelling of the legs is many times related to other, more serious causes (for example, heart failure, renal failure, or liver failure). 

Common causes of foot, ankle, and leg edema include:

• Blood pressure-lowering drugs.
• Body fluid overload.
• Burns.
• Certain antidepressants.
• Congestive heart failure.
• Diagnostic tests.
• Environment.
• Estrogens and progestin oral contraceptives.
• Extremity surgery.
• Generalized allergy.
• Glomerulonephritis or other kinds of kidney disorders.
• Infiltration of an intravenous site.
• Injury or trauma to the ankle or foot.
• Insect bite or sting.
• Long airplane flights or automobile rides.
• Long-term corticosteroid therapy.
• Medical treatments.
• Medications.
• Menstrual periods (for some women).
• Pregnancy (mild to severe swelling).
• Prolonged standing.
• Starvation or malnutrition.
• Sunburn.
• Testosterone.
• Venogram.
• Venous insufficiency (varicose veins).

You can mitigate swelling by elevating your legs above the heart while lying down. Avoid sitting or standing without moving for prolonged periods of time. Avoid putting anything directly under the knees when lying down, and don't wear constricting clothing or garters on the upper legs. 

Exercising the legs causes the fluid to work back into the veins and lymphatic channels so that the swelling goes down. The pressure applied by elastic bandages or support stockings can help reduce ankle swelling. A low-salt diet may help reduce fluid retention and decrease the ankle swelling.