Foot swelling that doesn't go away sometimes is a sign of a medical condition, such as a venous insufficiency, a blood clot, an injury or an infection, states WebMD. In pregnant women, some swelling of the feet and ankles is normal, but sudden, severe swelling sometimes indicates a serious condition known as preeclampsia. Underlying heart, liver or kidney disease and many medications, such as anti-inflammatory drugs and antidepressants, often cause swelling of the feet as well, states MedicineNet.
Venous insufficiency is a common condition in which some of the blood in the legs fails to travel back to the heart, explains WebMD. Normally, one-way valves in the veins keep blood in the lower part of the body flowing in an upward direction, but when these valves are damaged, blood begins to pool in the legs. This causes swelling in the ankles and feet.
Blood clots in the legs are either superficial or deep, explains WebMD. Superficial clots occur in the veins close to the skin and are rarely serious, but a deep clot, or deep-vein thrombosis, may be life threatening if it breaks off and travels to the heart and lungs. Signs of a deep-vein thrombosis include swelling in one leg or foot, discoloration in the area, pain and a low-grade fever.
If only one foot is swollen, it is likely the result of an injury or an infection, states MedicineNet. Injuries usually are accompanied by pain and localized swelling, while an infection usually causes redness, pain and, sometimes, an open sore. The infected area is also usually warm to the touch.