Swollen legs and ankles are often caused by standing or sitting for long periods, but persistent or recurring swelling may signal an underlying health condition. Known as edema, this occurs when excess fluid builds up in the body’s tissues. While temporary swelling usually improves with rest, ongoing or unexplained swelling should not be ignored, especially if it is accompanied by pain, redness, or other concerning symptoms.

One of the most common causes is poor circulation, which allows fluid to collect in the lower legs. Aging, prolonged inactivity, and vein disorders can all contribute to this problem. A high-sodium diet may also increase fluid retention, while varicose veins can cause swelling, aching, and enlarged veins due to weakened vein valves. Staying active, limiting salt intake, and drinking enough water may help reduce mild swelling in some cases.

Swelling can also be linked to more serious conditions affecting the heart, kidneys, or liver. Heart failure may reduce the heart’s ability to pump blood efficiently, while kidney and liver diseases can interfere with the body’s fluid balance. These conditions are often accompanied by symptoms such as fatigue, shortness of breath, chest discomfort, or unexplained weight gain and require prompt medical evaluation.

A particularly serious cause of sudden swelling is deep vein thrombosis (DVT), a blood clot that usually affects one leg and may cause pain, warmth, redness, and rapid swelling. Because a clot can travel to the lungs and become life-threatening, immediate medical attention is essential. If swelling persists, repeatedly returns, affects only one leg, or occurs with chest pain or difficulty breathing, seek medical care as soon as possible.