Your shoes feel tighter, your ankles look puffier, and your legs seem unusually heavy. It’s easy to blame a long day, but swelling deserves attention when it persists or appears without explanation. Fluid buildup, called edema, can affect one or both legs. NHS

Often, the explanation is ordinary: prolonged sitting or standing, salty food, or certain medications. Swelling alone cannot identify the cause, which is why a frightening headline should never be treated as a diagnosis. NHS

Sometimes, swelling is linked to vein problems or conditions affecting the heart, kidneys, or liver. If both legs remain swollen for several days or the swelling worsens, arrange a medical assessment. Unexplained swelling in one leg needs urgent attention, especially if it starts suddenly, hurts, or feels red and hot. NHS

There’s one combination that should never wait: swelling accompanied by breathlessness, chest pain, or coughing up blood. Call emergency services immediately. These symptoms can indicate a blood clot in the lungs or another serious problem. NHS

For mild swelling after prolonged sitting or standing, gentle walking and raising your legs may help. But recurring puffiness deserves an explanation. Notice when it begins, whether one or both legs are affected, and what other symptoms appear. Those details can help a clinician find the cause. NHS