Medically reviewed by Nachiket J. Patel, MD, FACC, FSCAI. Last reviewed July 2026.
Leg swelling is common, but the cause is not always obvious. Fluid may collect because of a vein problem, heart or kidney disease, medication, inflammation, injury, or impaired lymphatic drainage.
Whether swelling affects one leg or both, begins suddenly or gradually, and improves overnight provides important clues. Pain, skin change, breathlessness, and recent travel or surgery also matter.
At Flow Heart & Vascular, the evaluation is designed to identify the mechanism before recommending compression, a medication change, or a vein procedure.
What causes swelling in one leg?
A new one-sided change deserves particular attention because DVT must be considered. Long-standing one-sided swelling may still reflect treatable outflow obstruction or post-thrombotic disease.
- Deep vein thrombosis
- Chronic venous insufficiency
- May-Thurner syndrome or another venous obstruction
- Lymphedema
- Cellulitis or other inflammation
- Injury, joint disease, or a ruptured cyst
- A previous DVT with valve damage
What causes swelling in both legs?
Bilateral swelling may come from venous insufficiency, heart failure, kidney or liver disease, low protein levels, thyroid disease, lymphedema, or medication effects.
Some blood-pressure medicines, anti-inflammatory drugs, hormones, and other prescriptions can contribute. Never stop a medication on your own; the timing and alternatives should be reviewed.
When is leg swelling urgent?
Seek prompt evaluation for sudden one-sided swelling, particularly with pain, warmth, or redness. Call 911 if swelling is accompanied by sudden shortness of breath, chest pain, coughing blood, or fainting.
Rapidly worsening swelling with breathlessness at rest, inability to lie flat, confusion, or chest pressure can reflect acute heart failure or another emergency.
How is the cause diagnosed?
The examination looks at distribution, pitting, skin color and texture, varicose veins, pulses, wounds, heart and lung findings, and signs of lymphedema.
Venous ultrasound can check for DVT and reflux. Additional testing may include an echocardiogram, laboratory work, arterial testing before compression, or pelvic venous imaging when an outflow obstruction is suspected.
How is leg swelling treated?
Treatment depends on the cause. Options may include walking, leg elevation, appropriately fitted compression, skin care, medication adjustment, treatment of heart or kidney disease, venous ablation, or stenting of a significant venous obstruction.
Compression is not automatically safe for every patient. Significant arterial disease should be considered when pulses are weak, wounds are present, or symptoms suggest poor arterial flow.
A diuretic may help fluid overload from heart failure, but it does not correct venous reflux or lymphedema. Matching the treatment to the mechanism prevents frustration and unnecessary side effects.
Frequently asked questions
Why is swelling worse at the end of the day?
Gravity increases pressure in the leg veins during prolonged sitting or standing. Venous swelling often improves with walking, elevation, or overnight rest.
Can varicose veins cause significant swelling?
Yes, especially when the underlying vein valves allow sustained reflux. Ultrasound can show whether the visible veins are part of a larger problem.
Should I wear compression socks before being evaluated?
They help many venous conditions, but the strength and safety depend on arterial circulation, skin condition, and the cause of swelling.
Related heart and vascular information
Schedule an appointment
If you have a stable heart or circulation concern, request an appointment with Flow Heart & Vascular in Mesa, Arizona. Call 911 for emergency symptoms.
This page provides general education and does not replace individualized medical advice.
