Swollen Leg: Why One or Both Legs Swell and When to See a Doctor

A swollen leg is not a diagnosis but a sign: fluid is retained in the tissues, and the causes vary. Below — why a leg swells, what causes there are, and in which cases a visit to the doctor cannot be postponed.

Why one leg swells

Edema (oedema) is the accumulation of fluid in the tissues; most often it affects the feet, ankles, and lower legs, but it can also spread to the whole body. Swelling may be in one or both legs, including below, in the area of the foot and ankle. Signs of edema also include shiny or taut skin, a change in its color, dryness, discomfort, stiffness, and a mark that remains when pressed.

An analogy from mechanics: veins are the return pipeline to the heart pump. As long as the pipe is patent and the valves hold, fluid rises upward; when the lumen is compressed, a valve fails, or the pressure in the system has risen, fluid is retained at the lowest point.

Edema of one and both legs: when a doctor is needed

Edema may affect one or both legs. If both ankles, feet, or lower legs are swollen and the swelling has not decreased after home measures over several days, is worsening, or the person already knows about heart, kidney, or leg vein disease, a routine consultation with a doctor is needed.

Edema of one ankle, foot, or leg without a clear cause is a reason to seek urgent medical help.

Main causes of leg edema: veins, lymph, heart, injury

The list of causes is broad:

• prolonged standing or sitting in one position, excess salt, excess weight, pregnancy;
• medications: some blood pressure medicines, contraceptives, hormone therapy, antidepressants, steroids;
• varicose veins, thyroid problems, disorders of lymph node function, especially after mastectomy;
• injury — sprain of ligaments or muscles, insect bite, infection;
• disorders of heart, kidney, liver function (including cirrhosis), thrombus.

Edema after long walking in hot weather and after sunburn is mentioned separately. Swelling that looks the same may have both a harmless and a serious basis.

Edema with redness and pain: what these signs indicate

Redness and heat of the skin over the swelling are among the signs requiring urgent assessment; the cause is determined by a doctor. A leg that has swollen and hurts severely and suddenly also falls into this group.

For people with diabetes there is a separate rule: with edema of the feet, ankles, or legs they need an urgent consultation.

When leg edema requires urgent medical attention

An urgent consultation is needed for edema of one leg without a clear cause, for severe, painful, or suddenly onset swelling, for worsening edema after injury, for edema of the face or abdomen together with the leg, for redness or heat of the skin over the swelling, for high fever and chills.

Swelling of the leg by itself is not a reason to call an ambulance; 103 or 112 — if shortness of breath or difficulty breathing appears, a feeling of compression, heaviness, or pain in the chest, blood is coughed up, the heartbeat has become noticeable, dizziness, a near-fainting state, confusion, nausea, or clammy sweat have appeared: such signs may indicate a blood clot in the lungs and require immediate help.

The material is for reference: it describes possible causes of edema and does not replace consultation with a doctor — a diagnosis is not made from a description.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer